Preheat oven to 350 degrees. In a large bowl, mix together flour, baking powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer with paddle attachment (or in a large bowl, if using a hand mixer) cream together the butter and cream cheese until smooth. Add the granulated sugar and beat for 2 minutes until fluffy. Add eggs and vanilla, mix to combine. Alternating between the dry mixture, the lime juice, and the milk, add slowly to batter until fully combined. Scrape the sides as needed.
Fill mini cupcakes liners in a mini cupcake tin 2/3 of the way full. Bake for 11-13 minutes until a toothpick inserted into the center comes out mostly clean. A few small crumbs are okay, but any wet batter and they need longer. Place on a wire rack for 5 minutes to cool, pop out and place directly on the rack to cool completely.
Tequila Buttercream
In the bowl of a stand mixer with the whisk attachment (or a large bowl if using a hand mixer) cream the butter until smooth. Add the powdered sugar in a little at a time until incorporated, scraping sides as needed.
Add the vanilla and 3 tablespoons of the tequila, continue to mix. Beat for 2 minutes until fluffy. If the frosting seems a little thick, add the 4th tablespoon of tequila and mix to combine. Once the cupcakes are completely cooled, top with frosting.
Add the garnish of a small amount of kosher salt sprinkled on top and a gummy lime.
Notes
*If you don't want to use tequila, substitute another liquor, lime juice or milk.**Coarse raw sugar can be substituted here, or leave it off.***Fresh lime wedges can be used in the gummies place, or leave them off completely.