In the bowl of your stand mixer, or with a hand mixer, beat the butter until smooth. Add the vanilla extract and beat again. With the mixer on low speed, gradually add the sugar. Scrape down the sides of the bowl as needed. Add the milk and beat to combine. Once combined, beat the frosting on high speed until it is light and fluffy (about 5 minutes). If making ahead of time, be sure to cover to prevent the frosting from drying out. This frosting can be stored in the refrigerator for up to 10 days. Bring to room temperature & re-whip before using. Just add a little milk or sugar to get the right consistency. Can tint with food coloring if desired. This recipe makes enough to fill & frost one 8 or 9-inch cake, or 24 cupcakes.