In the bowl of an electric mixer fitted with the flat beater, beat the cream cheese on medium speed until smooth and fluffy, 2 to 3 minutes. Add the butter and continue to beat for 2 to 3 minutes more. Add the confectioners' sugar 1 cup at a time and beat until smooth and no lumps of sugar are visible. Add the vanilla and beat until combined. Makes 5 cups, enough to frost two 9-inch cake rounds or three 8-inch cake rounds.