These scrumptious, melt-in-your-mouth cookies tend to spread when cooking, but baking them in mini muffin tins keeps their shape. In testing, cookies made with Parkay-brand margarine spread much less; if using Parkay, you can drop or pipe the cookies directly onto the baking sheet.
Beat butter and sugar 3 minutes with an electric mixer at medium speed. Add extract; beat until blended. Add flour and cornstarch, beating until blended. Spoon or pipe dough into nonstick mini-muffin cups, filling one-third full. Bake at 350 degrees F 8 to 10 minutes, or just until edges begin to turn brown. Transfer to cooling racks; cool completely before frosting. Frost or pipe each cookie with a dollop of Peppermint Buttercream Frosting. Sprinkle with crushed peppermint candies.