Heat the oven and mix the cake batter as directed on the cake mix box. Spread it in a greased 9x13-inch baking pan and bake according to the box directions, about 28 to 33 minutes, until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 15 to 20 minutes.

While the cake is still warm, use the round handle of a wooden spoon to poke holes all over the top, about 1 inch apart and three-quarters of the way down. Wiggle the handle slightly to widen each hole.

In a medium bowl, whisk the instant chocolate pudding mix with 1 ½ cups of the milk for 2 minutes. Immediately pour it over the cake while it is still thin, spreading it with a spatula so it fills the holes. For more even stripes, pour the pudding into a squeeze bottle, cake injector or piping bag and fill each hole first, then spread the rest over the top.

Refrigerate the cake for at least 30 minutes, until it is cool to the touch and the pudding has set.

In a large bowl, beat the softened cream cheese and powdered sugar with a hand mixer until smooth and fluffy. Beat in the cocoa powder and the remaining 2 tablespoons of milk. Drop spoonfuls of the frosting over the cake and gently spread it into an even layer.

In another bowl, gently fold together the whipped topping, chocolate syrup and ½ cup of the chocolate chips. Spread it evenly over the frosting.

Sprinkle the remaining ¼ cup chocolate chips over the top and drizzle with the white chocolate sauce.

Cover and refrigerate for at least 4 hours, or overnight, before cutting into 12 squares. Serve cold.