for the cupcakes
Preheat oven to 350*F. Line the middle two rows of a muffin pan with cupcake papers (six total).
In a large mixing bowl, combine the flour, sugar, baking powder, and salt. Mix for a second or two to thoroughly combine the dry ingredients.
Add the stick of butter and half of the milk. Mix on medium-high speed for two minutes; the batter will be very fluffy. Scrape down the sides of the bowl with a spatula.
Add the egg whites and vanilla to the remaining milk and whisk to combine. With the mixer on low, slowly pour the milk into the batter. Raise speed to medium and mix until just combined.
Divide the cake batter among the six liners. Bake for 20-24 minutes or until an inserted toothpick comes out clean. Cool completely before frosting.
for the frosting
With the mixer on medium, beat the butter until it is very soft. Turn the mixer on low and slowly add the powdered sugar, beat until well-blended (if using a stand mixer, use the paddle attachment). Add the vanilla and salt and beat until incorporated. If the frosting needs to be thinned, add milk in half teaspoon increments until a spreading consistency has been reached.
If desired, tint with food coloring. Frost cupcakes and store in refrigerator. They should keep all week, resulting in a daily treat or dessert.
*Take the butter out of the fridge about 30 minutes prior to making the frosting to be sure it’s the proper temperature – you don’t want the butter bordering on melting or the consistency of the frosting will be off.