Bake the chocolate cake in a 9x13-inch dish following your batter’s directions. The top should look set, and the cake should feel soft but firm.
Let the cake cool for about 10 minutes. It should still be warm, not hot.
Use the handle of a wooden spoon to poke holes all over the cake. Space them evenly so the filling can spread through the cake.
Slowly pour the white cream filling over the cake. The filling should sink into the holes and soak into the cake.
Let the cake cool completely. The surface should no longer feel warm.
Spread the thick white cream topping over the top in an even layer. It should look smooth and fluffy.
Sprinkle crushed Oreo cookies over the top. Add whole or halved Oreos if you want more crunch.
Drizzle chocolate sauce over the top if using. Chill the cake before cutting so it slices clean.