Preheat oven to 350 degrees and line a cupcake muffin pan with 12 cupcake liners. Spray each with non-stick cooking spray.
In the bowl of an electric mixer, combine butter and sugar. Mix for 1 minute on medium.
Add eggs and vanilla and mix on medium for another 2 minutes, or until mixture becomes fluffy.
In a medium-sized bowl, combine flour, powder, soda and salt. Toss to combine.
Alternatively add dry ingredients and buttermilk into the butter/sugar mixture, starting and ending with the dry ingredients.
Lastly, mix in Margarita mix and lime zest until well combined.
Fill each cupcake muffin liner to ¾ full and bake cupcakes for 20-23 minutes, or until a toothpick inserted in the center comes out clean.
Immediately upon removing the cupcakes from the oven, brush each one with tequila.
Let cupcakes cool completely before frosting.