Combine butter and powdered sugar in a large bowl with electric mixer. Add vanilla and enough milk to make desired consistency. Beat for 1 to 2 minutes until very creamy. Spread over cake.
Browned Butter Variation: Heat butter in a small saucepan until well browned. Watch carefully so that the butter doesn’t burn. Cool at least 1 hour. Prepare frosting as above.
Raspberry Variation: Add 1/4 fresh or well drained frozen and thawed raspberries to butter and powdered sugar. Add 1 teaspoon vanilla extract and 2 to 3 tablespoons milk and prepare as above.
Peanut Butter Variation: Reduce butter to 1/4 cup and add 1/4 cup peanut butter. Prepare frosting as above.
Mint Chip Variation: Reduce vanilla to 1 teaspoon and add 1/2 teaspoon peppermint extract and a few drops green food coloring. Prepare frosting as above. Fold in 1/2 cup mini chocolate chips.
Cookies and Creme Variation: Prepare frosting as above. Beat in 1 cup coarsely crushed chocolate sandwich cookies. Spread frosting over cake and garnish with more cookies.