In a small bowl, mix egg whites, 1/4 cup of milk, and lemon zest. Set aside.

In a mixing bowl, beat butter and sugar until creamy, about 2-3 minutes. Add dry ingredients and mix until combined. Slowly add the egg white mixture and remaining milk. Mix until smooth.

Preheat the oven to 350°F. Fill cupcake liners halfway and bake for 15 minutes. Cool completely.

For the frosting, beat butter for 3-5 minutes until pale. Add powdered sugar, lemon zest, and lemon juice. Beat until fluffy.

Frost cooled cupcakes with lemon frosting. Serve and enjoy!