Strawberry Cupcakes with the *BEST* Rhubarb Buttercream

What is it about sitting at a desk that encourages one to work, to write? I don't know, but I am sitting here at my desk at home, knowing that it is the only way I will get this recipe out to you, and if I did not get this recipe out to you before strawberry and rhubarb season ended, it would be a travesty. 

So, as it happens, it's rather difficult to find a recipe for rhubarb buttercream. In fact, I could not, and had to create my own, but what's great about that is now it exists! And you, dear readers, can create it too. I was at the farmer's market in downtown PDX a few weeks ago, and had a shortbread cookie from Two Tarts Bakery (one of the few in this town that I think consistently turns out great cookies) and it was filled with a rhubarb buttercream - though that was closer in consistency to an Oreo cookie's filling. This deliciousness, tart and sweet, was the inspiration for the buttercream. I purchased the first strawberries of the Oregon season, some local rhubarb, and thought, Strawberry Rhubarb cupcakes it must be!

A long time friend and fellow baker, Nicole, gave me Martha Stewart's Cupcakes for a birthday a couple years ago. In there is a fabulous recipe for strawberry cupcakes, but it makes a ton. Well, if a ton was 30+ cupcakes. I did not need this kind of cupcake craziness, so I made a half batch, which ended up being 16 cupcakes. I will share my proportions below so you don't have to do the math yourself. I did nothing different than the recipe, and they were delicious. However, the icing, as mentioned above, was an entirely different story. So let's start with cake, then move forward, shall we?

You need: either three 6 cup or 1 12 cup and 1 6 cup (what I use) muffin tins. I don't like doing cupcakes in batches if I can avoid it, but if you only have one 6 cupper, as I assume is the case for many people, you can do this in batches, just keep your batter covered in between (damp dish towels are great for retaining moisture in a case like this), and in a cooler, sun-free (not the fridge) place. You need muffin cups too. I just stocked up on some from Cost Plus, very cute, with stripes and bright colors, which blow those pastel numbers from the grocery store out of the proverbial muffin liner water.

Recipe for 16 or so cupcakes

Preheat that oven to 350F.

Chop up your strawberries. 1 cup finely chopped. I used the food processor, because it makes a 15 minute job a 10 second job. Love that.

Sift your flours before measuring. Then sift them with your dries into a bowl:

1 and 1/4 cup (c from here on out) all purpose flour + 2 tablespoons (T from here on out)
1/4 c cake flour
1/2 T baking powder. You may protest that there is no such measure. I just wing this. A pinch difference in baking powder will be okay! Just fill your tablespoon measure halfway! Have faith in your eyeballing!
1/2 t salt (see that little t? that's for teaspoon) - I ground kosher salt very fine and used that. table salt works too, but you want a fine grain for cake. Pro tip, people. Learned it from a chef instructor, sharing it with you.

Set this aside and get out another bowl. These things I decide to bake always seem to use a ridiculous number of bowls and utensils. I am moving in two weeks to a house with a dishwasher, and I am pretty excited. It may lead to excessive baking. Instead of being the new neighbor who people bring pies to, I will be the new neighbor who brings everyone pies. And then, they will love me. But I digress. This is what happens when I try to write a recipe while hopped up on bubble tea. 

Cream together 1 stick room temperature unsalted (important, my friends) butter, 1c + 2T sugar (fine granulated works great in cakes) and 3/4t vanilla extract. I used the rum one from my homemade collection. Get this light and fluffy. The lighter and fluffier the better. You're aerating it, which makes for light cake! 

Okay, here's where dividing the measure gets a tad more complicated. You may want to have this at the ready before you cream together the above.  


Eggs. Room temperature eggs. Really, always do this. Run them under lukewarm water for a while if you have too. The people who eat your cakes will thank you. Dividing the recipe calls for 1 and 1/2 eggs, and 1/2 an egg white. How do you do this? Well, I will tell you. A large egg has about 4 T of stuff in it (stuff being yolk and white, of course). So, you crack one egg open, give it a twirl with a fork, then measure out two tablespoons of stuff. Voila, half an egg! So, math friends, that means 1 T egg white. Woo hoo. Enjoy that. So, after you've made that happen, add the one whole egg first, combine, then add the 1/2 egg + 1/2 egg white, and combine. Make sure everything on the sides of the bowl is incorporated into the mix. 

Next! Another slightly complicated maneuver, adding flour mix and milk, alternating.  Measure 1/2 c milk, room temperature (I just microwave it for 10 seconds to make this happen). You have that bowl of flour, so, while mixing, add in half the flour on low speed, then half the milk, then the rest of the flour, and the rest of the milk, until everything is combined. If it doesn't look like cake batter, keep combining, but on low speed please.

Finally, fold in that cup of strawberries. I have no picture of this. I do not know why. Do this by hand please, with your spatula.

Fill muffin cups slightly more than halfway and bake! I always shoot for the low side of the recommended time first, to ensure I don't over bake. Try 25 minutes. I think I took mine out at 27, and they looked still the slightest bit damp in the very centers, but they were fine. Use a toothpick to test one if you lack confidence in the doneness arena.

Okay, so the cupcakes are made! Woo hoo! But alas, you've only just begun! For the real bear here is that amazing rhubarb buttercream. It isn't easy, but it is SO worth the work. So next up:

 First, you need to roast your rhubarb. Cut it one pound of it into one or so inch chunks, spread it on a pammed baking sheet (I have a piece of silpat, but I senselessly did not use it here. If you do, you should), and lightly sprinkle with sugar (about 1/3 c). This will impact the overall tartness of your buttercream, so keep that in mind as you are sugaring it. Roast at 350 for 25 minutes until it's soft. 

When it comes out of the oven, let it cool just a bit, then puree it in your blender.

This is where it gets fun, and by fun, I mean tedious. You have to sieve the puree to make it smooth. You may need a friend's help, I certainly did. Pour the puree into a small holed metal colander (the ones that look like a screen door in a bowl shape), and press it through into a bowl. I used a rubber spatula to help this process along. 

It wants to stay adhered to the outside of the metal, so your friend can use a second spatula to coax it into the bowl. After all this ridicuous work, you'll have about a 1/2 c. rhubarb puree (f you're making a whole batch of cupcakes, instead of a half batch, I'd double this). Good times, good times. Set that aside for the moment. You will be tired. You may want to rest, because this icing isn't exactly a cakewalk either.

You might be wondering how I got this idea for adding rhubarb puree into icing. Well, I was reading the awesome Cake Bible for my icing recipe, and it provides advice on how to make strawberry icing. I figured that if I just made a puree and used that in place of the strawberry measure, it would do the same thing. I was right. 

Okay so the icing. This is an adaptation of the Cake Bible's classic buttercream on p 228. It is without a doubt the best icing I've ever made. I'm not kidding. I will be making it again. And again. And again. So, you're going to need a candy thermometer to be able to make this icing, because it involves boiling sugar water to a specific point. You will also definitely need either a friend holding your mixer, or a KitchenAid Mixer. The latter will make this icing truly magnificent, so you know, get started on your Christmas list. Again, I reduced this to make half the recipe. The whole recipe will ice an entire cake. Pam or butter a heatproof pyrex cup measure, keep it near the stove. 

 Beat three egg yolks in the mixer until they are light. Only the yolks. Surely we've discussed separating eggs before, but if not, just to let you know, I do this with my hands. Just open the cracked egg into your hand and let the egg white slip through your fingers, and be really careful when you pull that little white thing that's on some eggs off, because your yolks may suddenly spill out too. 

In a very small saucepan, combine 1/2 c sugar and 1/4 c water, mix until it dissolves, then bring to a boil while constantly stirring. Stop stirring when it boils, and put the candy thermometer in there until it reads 238F. This is kind of challenging, because you want the temperature of the syrup, not the pan. I have to tilt it to do this. Be careful though, sugar burns are the worst. When that thermometer reads 238, pour the syrup in that waiting measure. Pour a little syrup over the yolks, turn on the mixer, and beat for a few seconds (this is kind of a quick temper). Stop the mixer, add a little more syrup, repeat. Do this a few times until you've poured out all the syrup, using a spatula to get the rest out on the last addition. Be forewarned: I didn't grease my measuring cup, and my syrup starting sticking as it was becoming candy during this process. Then keep beating the sugar egg mixture until it is cool. This is why you're glad you have the KitchenAid. 

Beat in 2 sticks (!!) unsalted room temp butter, add in chunks. Then finally, add in your puree. The reduction would suggest I only add in 1/4 c, but I had just under 1/2 c, and I was loving the color and flavor it was imparting, so I added it all. I tasted it, and it was magnificently tangy! Maybe too tangy. Puckering over icing, not so much. So, I added in a little powdered sugar, and finally added about 1 cup. Now this, this, was magnificent icing. 

I think next time I make this (tomorrow, as I am making icing to teach a special small friend how to decorate cakes on Thursday) I will add in some vanilla, and also play some more with the powdered sugar and see what I can make happen. So really, that's it! These were truly awesome cupcakes. Definitely try this early summer treat, you'll thank yourself for all that effort, and maybe your true love will do the last batch of dishes, as mine did. --T


1 comment:

Heather said...

So funny! I search for "rhubarb buttercream" and the first site that I come across is a fellow PDX foodie! Using your recipe for the filling for a macaron. Will be checking back on your culinary adventures!

: )