In a stand mixer bowl, add the room temperature butter and the shortening. Using a paddle attachment, mix at medium speed. Once the mixture is a pale yellow color and nice and creamy in texture, add the vanilla and mix again.
Slowly, start to add the confectioner's sugar in about four batches. Mix well after each addition at a low speed. Stop and scrape the bowl with a spatula in between additions. The frosting will seem fairly dry at this point, but use all the powdered sugar.
Next, add one or two tablespoons of milk at a time, mixing well after each addition at medium speed. How much milk you use will depend on how thick you want your frosting. (Tip: if you are using a liquid food coloring, add a bit less milk.)
Once you have the frosting to your preferred consistency, it is ready for coloring and frosting your baked goods.
Store the frosted goodies and any leftover frosting for up to three days at room temperature. Otherwise, place in an enclosed container for up to two weeks in your refrigerator. You can also freeze the frosting for up to 6 months.
Notes
• This batch makes about 6 cups of frosting, which is enough to do either one 3-layer 8" or 9" cake, one 9 x 13" sheet cake, or about 24 to 36 cupcakes.• Nutritional value is per cup of frosting.