For the cupcakes: Preheat oven to 350℉. Line a 12-cup muffin pan with paper liners and lightly grease the top of the pan with nonstick cooking spray.
Spoon batter into prepared muffin pan. Fill each cup about ⅔ full.
To make the vanilla frosting: Mix softened butter until light. Add powdered sugar, milk, and vanilla extract. Mix until fluffy If frosting is too thin, add more powdered sugar. If it’s too thick, add a little more milk.
Frost cupcakes when they’re totally cool. Store leftover cupcakes wrapped on the counter for up to three days.