Taken from Annie's Eats
Makes about 24 cupcakes
3 C all-purpose flour
1 Tbsp baking powder
1/2 tsp salt
1 C unsalted butter, at room temperature
2 C sugar
4 large eggs, at room temperature
3 limes, zested and juiced
1/2 tsp vanilla extract
1 C buttermilk
2 C sugar
8 large egg whites
Pinch of salt
1 1/2 C unsalted butter, at room temperature
2 1/2 Tbsp freshly squeezed lime juice
4 Tbsp tequila
For the Cupcakes:
Preheat the oven to 325˚ F. Line two cupcake pans with paper liners.
In a medium bowl, combine the flour, baking powder and salt; stir with a fork to blend.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar on medium-high speed until light and fluffy, 3-5 minutes. Blend in the eggs one at a time, mixing well after each addition and scraping down the sides of the bowl as needed. Beat in the lime zest, lime juice and vanilla.
With the mixer on low speed, mix in the dry ingredients in three additions alternating with the buttermilk, beginning and ending with the dry ingredients. Beat each addition just until incorporated.
Divide the batter between the prepared cupcake liners, filling each about 3/4 full.
Bake 20-24 minutes, or until a toothpick inserted in the center comes out clean. Let cool in the pan 5-10 minutes, then transfer to a wire rack to cool completely. If desired, brush the cooled cakes with tequila to emphasize the true margarita flavor.
To make the frosting, combine the sugar, egg whites, and salt in a heatproof bowl set over a pot of simmering water. Heat, whisking frequently, until the mixture reaches 160° F and the sugar has dissolved.
Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment. Beat on medium-high speed until stiff peaks form and the mixture has cooled to room temperature, about 8 minutes.
Reduce the speed to medium and add the butter, 2 tablespoons at a time, adding more once each addition has been incorporated. If the frosting looks soupy or curdled, continue to beat on medium-high speed until thick and smooth again, about 3-5 minutes more (don’t worry, it will come together, though it may take a long time!) Stir in the lime juice and tequila and mix until fully incorporated and smooth.
The cake part of the cupcakes were really easy to make and super-tasty. I did drizzle a bit of tequila over the top of each cupcake before frosting. It added to the flavor.
The frosting was when I started to loathe these cupcakes. After lots of careful thinking, I blame step one of the frosting directions. I either over-heated or under-heated the egg and sugar mixture. I need to invest in a candy thermometer. Nevertheless, I tried to recover from my error by really, really beating the frosting. Think 30 minutes on high in the Kitchenaid. I may have actually over-mixed it. It was runny. It seemed like a good idea to add some cream of tartar to try to save it. That didn't work. It seemed like a good idea to harden it in the freezer. That worked - until I started beating it to make it smooth again. I ended up freezing it and then piping it on to the cupcakes as quickly as possible. The cupcakes had to be refrigerated or the frosting would soften and ooze off of the cakes.
It was incredibly frustrating to say the least, but the frosting - no matter how runny - did taste pretty good.