Preheat the oven to 325 degrees F. Line 2 standard muffin tins with 16 paper liners and set aside.
In a medium bowl, whisk together the flour, baking powder and salt.
In an electric mixer fitted with the paddle attachment, beat the butter and sugar together until pale, light, and fluffy, about 5 minutes.
Reduce the mixer speed and add the eggs one at at time, mixing thoroughly after each addition.
Scrape the sides of the bowl and add the lime zest, lime juice, vanilla extract and tequila. Mix until combined. The mixture may start to look curdled at this point, but don’t worry, it will all come back together.
Add the dry ingredients in three batches, alternating with the buttermilk in two batches. Mix only until just incorporated, using a rubber spatula to give it one last mix by hand.
Divide the batter between the muffin cups, filling about 2/3 of the way. Bake for approximately 25 minutes or until just slightly golden and a toothpick comes out clean, rotating the pans halfway through baking.
Allow cupcakes to cool for 5 to 10 minutes, and then remove to a cooling rack. Brush the tops of the cupcakes with the 1 to 2 tablespoons of tequila. Set the cupcakes aside to cool completely before frosting them.
To make the frosting, beat the butter in the bowl of an electric mixer fitted with the paddle attachment for 5 minutes. Reduce the speed and gradually add the powdered sugar, mixing and scraping the sides of the bowl until all is incorporated. Add the lime juice, tequila and salt. Mix until incorporated and fluffy (it will increase in volume as air is whipped into it). If the frosting appears a bit too soft, add some additional sugar or refrigerate briefly to firm up. Frost cupcakes and garnish, if desired, with lime zest, an additional sprinkling of salt and/or a lime wedge.