1/2 c. butter
1/2 c. shortening
1 1/2 tsp. vanilla
5 c. sifted confectioners' sugar (or 1 box)
3 tbsp. milk (+ 2 tbsp. milk)

Cream butter and shortening. Add vanilla. Add sugar, 1 cup at a time. Beat well medium. Add milk. Beat high until fluffy.