In the bowl of a stand mixer, cream the butter until nice & smooth. Whip in the sugar, creaming until evenly combined and smooth. Beat in a single egg at a time, until the mixture's smooth and completely incorporated.
1/2 cup salted butter, softened, 2/3 cup granulated sugar, 3 eggs room temperature
Add the flour, baking powder, and salt. Mix slowly and carefully, just until evenly combined. Stir in the margarita mix and zest, just until evenly incorporated.
1 1/2 cups flour, 1 1/2 tsp baking powder, heaping 1/4 tsp salt, zest of two fresh limes
Add 12 cupcake liners to a cupcake pan. Fill each liner 2/3 of the way full with the batter, repeating until all are filled.
Bake the cupcakes at 350 degrees for 18 minutes. When the cupcakes are done, remove them from heat and let them cool 5 minutes, before removing to metal cooling racks to finish cooling completely.