Recipe courtesy of Trophy Cupcakes
1. Preheat the oven to 350 degrees F. Line two 12-cup muffin pans with cupcake liners and set aside.
2. Zest the limes and set zest aside. Juice 1/4 cup lime juice and set aside.
3. In a large bowl, sift together the cake flour, all-purpose flour, baking powder, salt, and baking soda. Set aside.
4. Combine the buttermilk and lime juice in a large measuring cup with a spout. Set aside.
5. Combine the lime zest, butter, and sugar in the bowl of a stand mixer fitted with the paddle attachment and beat them at low speed until the mixture is smooth and creamy, about 1 minute if the butter is soft. If the butter is cool, it will take longer. Add the eggs one at a time, mixing well and scraping the bowl after each addition, and waiting until all traces of each egg have disappeared before adding the next one.
6. Add the dry ingredients in 3 parts, alternating with adding the wet ingredients in 2 parts. Keep the mixer at the lowest speed, and mix each time just until the ingredients are combined. When everything has been added, scrape the bowl and paddle one more time, and stir the batter just until it’s smooth. Let the batter rest for 15 minutes and stir gently before using.
7. Fill the cupcake liners three-quarters full and bake until the tops of the cupcakes are firm and a cake tester inserted in the center of a middle cupcake comes out with just a few crumbs, about 20 minutes. Let the cupcakes cool for 5 minutes in the pans before removing to a rack to cool completely.
1. Zest the limes and set zest aside. Juice limes and set aside.
2. In a stand mixer fitted with the paddle attachment, cream the butter. Start with the mixer at the lowest speed, then gradually increase the speed, using a rubber spatula to scrape the bowl as needed, until the butter is light in color, perfectly smooth, and makes a slapping sound as it hits the sides of the bowl. If the butter is soft, this should only take 30 seconds, but if the butter is cool, it can take a couple of minutes. Add the sour cream and mix until smooth.
3. Add the sugar, 1 cup at a time, and mix at the lowest speed until it’s fully incorporated before adding the next cup. When all the sugar has been added, scrape the paddle and the bottom and sides of the bowl. Add the tequila, lime juice and zest, and lime oil, and beat them at low speed for 15 seconds. Increase the speed to as high as you can without making a mess and whip the buttercream until the mixture is perfectly smooth, creamy, and light, about 5 minutes. Stop the mixer once or twice to scrape the bowl and paddle, then continue beating. At first the buttercream will appear to soften, then it will stiffen and increase in volume.
4. Use right away, or store in an airtight container for up to a week in the refrigerator.
When you’re ready to use it, let the buttercream come to room temperature if possible, then put it back in the stand mixer and use the paddle attachment to beat it until it’s creamy and stiff again.
For candied citrus peel:
Peel limes and cut into ½-by-2-inch strips.
Place peel in a small saucepan and cover with cold water. Bring to a boil, then drain and rinse with cold running water. Repeat process 2 more times, using fresh water.
In a separate saucepan bring the sugar and water to a boil. Stir until the sugar dissolves, then add the blanched citrus peel. (If you are using larger fruits, double the sugar syrup or just use the peel from 1 fruit.)
Bring syrup and peel to a boil and reduce heat to a simmer. Cook peel until tender and translucent in color, about 10 minutes.
Remove from heat. Cool slightly, then remove peel with a slotted spoon or tongs.
Lay peel on a wire rack to cool—placing a cookie sheet or parchment paper beneath the wire rack for easy cleanup—then toss in sugar until well coated. Transfer candied peel to an airtight container and store at room temperature for up to 1 month.