Mint-Filled Chocolate Thumbprints... Mint-Filled Chocolate Thumbprints Ingredients Cookies 1/2 cup granulated sugar 1 cup butter or margarine, softened 1 teaspoon vanilla 1 egg yolk 1 1/2 cups Gold Medal® all-purpose flour 1/4 cup unsweetened baking cocoa Mint Filling 1/4cup butter or margarine, softened 1 cup powdered sugar 1 tablespoon milk 1/4 teaspoon peppermint extract 2