Mix butter and shortening in large mixing bowl in a electric mixing bowl.

Add vanilla and salt.

Gradually add sugar one cup at a time.

Srape bottom and sides of bowl often. when all sugar is added icing will appear dry.

Add milk and beay at high speed until light a fluffy.

Keep icing covered with a damp cloth untill your ready for it.

For best results keep icing refrigerated

By the way this is from a real bakery. My grandma worked in bakery before she passed away and i got this recipe from her storge bin she kept with her baking stuff before she passed she gave me all the things on the bin which was tons of cool stuff bakers use everyday! I still have it i hope u enjoy this recipe as much as i do.