For the cake: Spray a 9-by-13-inch cake pan with cooking spray.
Bake the cake in the prepared pan according to the package instructions. Allow to cool slightly, then, using the handle of a wooden spoon, poke holes all over the cake.
Melt the chocolate chips in a medium microwave-safe bowl in the microwave in 20-second increments, stirring between each, or in a double boiler on the stove, until smooth. Add the condensed milk and milk, then stir to combine. Slowly pour the mixture over the cake, ensuring you hit every last inch. Allow the mixture to soak into the holes while you make the frosting.
For the frosting: Combine the milk, pudding mix and cocoa powder in a bowl. Whisk the mixture until it thickens, 1 to 2 minutes. Gently fold in the whipped topping until combined well.
Spread the frosting over the cake, then decorate with the cherries, if using. Enjoy.