You can't have a great cake with out great icing! So, here is how I make my buttercream frosting!
Toss your butter in a mixing bowl.
Add your shortening.
Add your salt, vanilla and mix.
Put the cover on (if you have one) and begin to add small amounts of powdered sugar and milk.
If you don't have a cover just wrap a kitchen towel around your mixer to helps keep the powdered sugar in the bowl.
Beat on medium for a couple minutes until nice and fluffy!