Peanut Butter Buttercream Frosting

• 3/4 cup vegetable shortening • 3/4 cup salted butter - softened • 1 cup creamy peanut butter (more if you want a stronger peanut butter flavor) • 2 teaspoons of vanilla • 6 - 8 cups (approx. 1 ½ - 2 lb.) powdered sugar • 6 - 8 tablespoons milk