Key Lime Cupcakes

When the key lime tree growing in a pot in front of our house is bursting with fruit like it is right now, it means only one thing to me: time to make key lime cupcakes! This year I’ve got all sorts of other key lime ideas (key lime tiramisu, key lime cookies, key lime pie, key lime ice cream, the possibilities are endless!), but I had to start with my classic favorite cupcakes. These cupcakes aren’t difficult to make, but they are definitely a bit time-consuming. I’ve had some health issues this year that have kept me from baking as often as I like due to mobility problems, so now that I am feeling better most days I have been itching to get back in there. This recipe is great for that because of the different steps; they took me two days to finish this time, but I got to rest in between. Plus, they are totally worth waiting for, if I do say so myself (and I do).

I made this recipe up because the key lime cupcakes I had had from various bakeries and found in various cookbooks just weren’t…key-lime-y…enough for me. I like a seriously tart dessert with tons of delicious citrus flavor, so I was intent on infusing every part of this treat with some lime component. I started with my favorite yellow cake recipe, taken from Cupcakes! and adapted it slightly by using a bit less sugar and adding a generous amount of key lime zest to the batter. Elinor’s recipe is so great in part because it uses only oil as the fat, no butter, so it can be used last minute instead of having to wait for butter to soften. The first time I made it I worried it would have an effect on the cake but they always, always come out moist and delicious. So, I start by making regular sized cupcakes, adding the key lime zest to the batter at the very end. Using an ice cream scoop sprayed with cooking spray, I divvy the batter up in the cupcake pans and pop them in the oven.

While the cakes are baking, I make the key lime curd that I use as a filling. This recipe I took directly from Cupcakes: Luscious bakeshop favorites from your home kitchen cookbook, and it NEVER fails to turn out perfectly. Seriously, why anyone pays the high prices for jarred curd when it is this easy to make baffles me. Well, aside from the fact that people just don’t realize how easy it is! Here is the recipe* (it can be altered to make a citrus curd of any flavor; just change up the juice!):

Ingredients:
4 tbsp key lime juice
½ cup sugar
4 egg yolks
½ tsp salt
4 tbsp butter
2 tsp key lime zest

Directions:
1. Combine the juice, sugar, egg yolks, and salt in a heavy bottomed sauce pan and put over medium to medium-high heat.
2. Whisk mixture over the heat constantly for 5-8 minutes or until mixture is thick enough to coat the back of a spoon. Do not allow the mixture to boil or it will curdle.

3. Remove pan from the heat and add butter, one tablespoon at a time, whisking until each piece is fully melted before adding the next.
4. Strain mixture through a fine-mesh sieve to remove any lumps (I consider this an optional step; I have never done it because I have never had a lumpy mixture).
5. Stir key lime zest into the mixture, then pour into a container and press plastic wrap over the surface before putting on the lid. Put container in the fridge to continue setting for at least one hour.

*This recipe was re-written in my own words from memory, so any mistakes are my own!

The only difficult part of this recipe is keeping your whisking arm going for 5-8 minutes; I switch off because I am a wuss.

For the frosting, I use a basic buttercream (powdered sugar, softened butter, vanilla extract) and add key lime juice to the mixture. I normally dislike the potent sweetness of this type of buttercream (I prefer the style made with egg whites), but the citrus juice mellows it out quite a bit. Sometimes I’ll add additional zest to the frosting as well.

My favorite part of these cupcakes is the filling, so I tried several ways of filling these to find the optimal way to get the best proportion. While it is more time-consuming than using a cupcake filler or a pastry bag with a round tip, I’ve found that the “cone” method is the best way for filling these cupcakes. Feel free to do it any way you want, though, of course!

To fill the cupcakes, I start by using a short sharp knife (if it has a name, I have no idea what it is; it’s the smallest one in my knife block) to angle into the top of the cupcake, moving the knife all the way around in a circle. See here:

I then remove the cone of cake from the cupcake and slice off as much of the pointy part as I can while still keeping the top part intact. See?

Then, I replace the top portion of the cone on the cupcake. Once every cupcake as been coned and re-topped, I go back and fill each cupcake with my chilled key lime curd; each one holds about a teaspoon to a teaspoon and a half of filling.

Once each cake is filled, I put the top back on (each one has to be topped as they are filled or I have a tendency to forget which top goes with which cake!). Then, once the cakes are all filled, I put them on a platter and stick them in the fridge while I make the frosting. Chilling them helps them set up better so that the tops don’t slip at all when frosting.

These cupcakes are pretty simple but delicious and just scream summer to me. Plus, there are so many cute ways to decorate them; I was out of piping bags yesterday, though, so I just did something basic.