In a large bowl, cream the butter, cream cheese and sugar until light and fluffy. Add 1 egg at a time, beating well after each addition. Beat in vanilla. Add flour until well blended. , Pour into a greased 15x10x1-in. baking pan. Bake at 325° until a toothpick inserted in the center comes out clean, 30-35 minutes. Cool completely on a wire rack. , For frosting, in a small saucepan, combine sugar and milk; bring to a boil over medium heat. Cover and cook for 3 minutes (do not stir). Stir in butter and chocolate chips until melted. Cool slightly. Stir frosting; spread over top of cake. If desired, top with sprinkles.