White and Dark Chocolate Cream Cheese Chocolate Cake Bars

box devil’s food cake chocolate cake mix (or your favorite boxed chocolate cake mix)

unsalted butter (1 stick), softened

large egg

vanilla extract (bourbon vanilla is especially nice)

to 2 tablespoons cold brewed coffee or water, optional if necessary

semi-sweet chocolate chips

white chocolate chips

sweetened condensed milk

cream cheese, softened (I use whipped cream cheese)

vanilla extract (clear imitation vanilla extract will keep this layer whiter)