For the cupcakes:
3 cups flour
1 tbsp baking powder
1/2 tsp salt
1 cup (2 sticks) unsalted butter, softened
2 cups granulated sugar
4 eggs, at room temperature
3 limes, zested and juiced
1/2 tsp vanilla
1 cup buttermilk (or 1 cup milk + 1tsp lemon juice)
1/2 cup tequila
1/4 cup Triple Sec

For the tequila-lime buttercream:
2 cups granulated sugar
8 egg whites
3 sticks butter, softened
2-1/2 tbsp lime juice
1-2 tbsp tequila