Store Bought Buttercream Extender By zoraya recipe Comments | 0 Favorites | 71 Start with a can of store bought icing and “extend” it for a yummy homemade version of buttercream. Store Bought Buttercream Extender Ingredients 3-4 c. powdered sugar1 stick butter1 c. crisco1-2 tsp. vanilla or orther flavoring1 can ready made frosting Instructions Mix the butter and crisco first in a mixer and then add other ingredients. Mix on low until completely blended. Takes color well. Makes a medium consistency icing good for piping stars.