Chop the bittersweet chocolate bar and set aside.
In a medium sauce pan mix the cornstarch, sugar and salt.
Combine the milk and heavy cream in a measuring cup with a spout.
Over medium heat, slowly stream in the milk and cream while whisking until it starts to thicken. This part is important as the milk and cream can burn quickly, you have to watch and whisk the entire time until it’s thick.
Add the chocolate to the mixture and continue to stir.
Add in the vanilla extract and keep whisking. Once the mixture is thicker and coats the back of a spoon, the pudding is done. Pour into a heat-proof bowl.
Push saran wrap all the way down so it’s touching the pudding. You want the saran wrap to cover the actual top of the pudding and then put in the refrigerator.
Let it cool and thicken for a few hours or overnight.
Scoop pudding into a small glass. A 4-ounce or 6-ounce glass works great. The amount of pudding you add will vary depending on your glass size. Leave room at the top for the Oreo cookie crumble.
Add a nice layer of crumbled Oreos over the top of the pudding. Wiggle the tombstone into the pudding.
Make everything the day before, but assemble the day of.