In the bowl of your electric mixer, or with a hand mixer, beat the butter until smooth and well blended. Beat in the vanilla extract. With the mixer on low speed, gradually beat in the sugar. Scrape down the sides of the bowl as needed. Add the milk and beat to combine. Then, on high speed, beat frosting until it is light and fluffy (about 5 minutes). If not using right away, cover with plastic wrap to prevent the frosting from drying out.
This frosting can be stored in the refrigerator for up to 10 days. Bring to room temperature and re-whip before using. Add a little milk or sugar if needed to get the right consistency.
Tint portions of frosting with desired food color (I use the gel paste food coloring that is available at cake decorating stores and party stores).
To make a Chocolate Frosting prepare the above recipe but beat into finished frosting, four ounces (120 grams) of melted and cooled unsweetened chocolate. Add a little extra milk if needed
This recipe makes enough to fill and frost one 8- or 9- inch (20 - 23 cm) cake.
Note: For a softer and fluffier frosting use a combination of 1/2 cup (113 grams) unsalted butter and 1/2 cup (113 grams) shortening.