1. Cream your butter and shortening until well incorporated. Both must be at room temperature to prevent clumping.
2. Once creamed, add your vanilla and mix again.
3. Slowly add in your powdered sugar.
4. Once you add all your powdered sugar, then add in milk slowly one tbsp. at a time.
5. How firm you want your buttercream will depend on if you add 4 or 5 tbsp.
6. Be sure not to over-whip your buttercream, normally a buttercream recipe says to whip until light and fluffy.
7. For my recipe you want to mix until it is creamy and smooth. Maybe two minutes. If you over-whip it will be grainy.
8. After piping your buttercream, allow 6-8 hours to dry before stacking. The shortening allows your buttercream to form a crust, but not hard like Royal Icing.
9. Store unused buttercream in the fridge for about a week.