Buttercream icing

I am looking for the best buttercream icing, that does not crust or get hard. . I was told to add crisco to my recipe to keep it soft.And it does work, but I don’t think the professional bakers use that method. Can anyone help me?

BUTTERCREAM FROSTING

1 stick (1/2 cup) butter or margarine, softened
1/2 cup vegetable shortening
1 tsp. vanilla
1 1/2 cups confectioners’ sugar
3 to 6 tablespoons of cold milk

Cream the butter and the vegetable shortening until its fluffy. Mix in the vanilla. Gradually add the confectioners sugar beating well (use an electric). Add milk and continue to beat. Whip until fluffy. add the 3 tablespoons of milk and see if its to your liking add more milk until the thickenss is just right. Frosting is ready to use.
this is how I made mine and it was given to me by a backery in ontario, California
I have to make sure my cake is ready to frost or my family eats it with a spoon. And I do have to admit I do too LoL…