In a large bowl, mix together lime juice, lime zest, milk, oil, tequila, vanilla, and sugar.
In a small bowl, mix together flour, baking soda, baking powder, and salt.
Add the dry ingredients to the lime mixture and stir until just combined.
Divide evenly among 18 cupcake liners.
Bake at 350 F for 20-24 minutes, until a tester comes out clean and the cupcakes spring back when lightly pressed.
Beat butter on high speed with an electric mixer for about three minutes until light and airy.
Mix in powdered sugar a little bit at a time.
Add lime zest, tequila, and salt and continue to beat for another minute.
Pipe onto cooled cupcakes.
Optionally, mix coarse sugar and kosher salt together in a small bowl in a 3:1 ratio and sprinkle over the tops of the cupcakes.
The cupcake recipe (not the frosting) originally came from the vegan cupcake cookbook called Vegan Cupcakes Take Over the World.Cupcakes last for two days at room temperature or up to five days in the refrigerator.