How to Make It
Make the cupcakes: Heat oven to 350° F. Line a standard 12-cup muffin tin with paper liners. In a medium bowl, whisk together the flour, lemon zest, baking powder, and salt; set aside.
Using an electric mixer, beat the butter and sugar on medium-high until fluffy, 2 to 3 minutes. Beat in the eggs, one at a time, then the vanilla, scraping down the sides of the bowl as necessary.
Reduce mixer speed to low. Add the flour mixture in 3 additions and the milk in 2 additions, beginning and ending with the flour mixture. Mix just until combined (do not overmix).
Divide the batter evenly among the muffin cups. Bake until a toothpick inserted in the center comes out clean, 15 to 20 minutes. Cool in the tin for 10 minutes, then transfer to rack(s) to cool completely.
Make the frosting: Using an electric mixer, beat the butter and sugar on medium-high until light and fluffy, 3 to 5 minutes. Beat in the lemon zest, juice, and salt. Frost the cupcakes.