Prepare eight 6–8-ounce clear dessert cups.
Finely chop the semisweet chocolate.
Whisk sugar, cocoa powder, cornstarch, and salt in a saucepan.
Gradually whisk in the milk until smooth.
Cook over medium heat, whisking frequently.
Once gently bubbling and thickened, cook for about 1 additional minute while whisking.
Remove from heat and add chopped chocolate.
Whisk until completely melted.
Stir in butter and vanilla.
Transfer to a bowl, cover the surface, and refrigerate for at least 2 hours.
Roughly crush the chocolate sandwich cookies.
If desired, decorate rectangular tombstone cookies with a small amount of melted chocolate and allow them to set.
Add a layer of chocolate pudding to each serving cup.
Sprinkle with crushed cookie dirt.
Add another layer of pudding.
Cover the surface with additional crushed cookies.
Insert one tombstone cookie into each cup.
Partially bury one or two gummy worms in the cookie crumbs.
Add a final scattering of coarse cookie crumbs.
Refrigerate until serving.