Bake the cake as instructed on the box in a 9×13 dish.
Once it is cooked, remove from the oven and let sit for about 5 minutes.
While it’s still cooling and slightly warm, poke holes throughout with a wooden or plastic spoon end.
Make pudding as directed.
Immediately after mixing the pudding, pour it onto the cake (don’t let it get as quite as thick as pudding usually is).
Spread the pudding around so it fills in the holes.
Place the cake in the fridge until the pudding gets firm.
Ice the cake and add sprinkles.