In small bowl, mix egg whites, 0.25 cup of whole milk, and lemon zest. Set aside.

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

Prepare cupcake tins with paper liners. Fill liners half full and bake in a 350°F oven for 15 minutes. Remove and cool in pan 5 minutes then transfer to cool completely on a wire rack.

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

Frost cooled cupcakes with lemon buttercream using a piping bag. Serve and enjoy!