1/2c real butter
4 c powdered sugar-sifted
few drops of clear butter flavoring (or more depending on your taste)
3oz (6T) heavy whipping cream
cream shortening and butter til fluffy. add powdered sugar about a cup at a time, mix until smooth and creamy. add vanilla, mix. add cream 2T at a time and mix well after each addition. add butter flavor, mix well. Add more powdered sugar if you need a more stiff icing.
You can google buttercream recipe and find a million different combos, I combined a few different ones I liked and came up with the recipe above.