Preheat oven to 175°C (350°F). Grease a 12-cup muffin tin.
Whisk flour, baking powder, and salt. Set aside.
Beat butter and sugar until fluffy, about 3 minutes. Add eggs one at a time, then vanilla.
Alternate adding dry ingredients and milk in three additions. Fold in lemon zest or sprinkles.
Fill molds two-thirds full. Bake 16-18 minutes until a toothpick comes out clean. Cool completely.
Beat butter until fluffy. Add powdered sugar, cream, and vanilla. Beat until slightly stiff.
Brush cooled cakes with simple syrup. Frost and decorate. Wrap individually to transport.