This is a super simple and very delicious icing that works great for cakes and cookies. If you want to color this frosting paste or gel works better. Liquid food coloring will probably require you to add more confectioner's sugar.
1/2 cup shortening
1/2 cup butter, softened
1 teaspoon vanilla extract
4 cups confectioner's sugar
2 tablespoons milk
In a large bowl, cream together the butter, shortening, and vanilla. Add in the sugar beating well. Beat in the milk, and continue mixing until light and fluffy. Keep icing covered until ready to decorate.
For chocolate buttercream: add 3/4 cup cocoa or three 1 oz. unsweetened chocolate squares, melted (will need to increase the amount of milk to about 3-4 tablespoons); peanut butter buttercream: decrease the shortening & the butter to 1/3 cup and add 3/4 cup peanut butter (will also need to increase the milk to get the right consistency); replace the vanilla extract with maple, almond or your favorite flavors. The possibilities are endless.
Keep leftover icing refrigerated for several days. Frozen in an air tight container for several months.