Make the Chocolate Pudding
In a medium saucepan, whisk together sugar, cocoa powder, cornstarch, and salt.
Place over medium heat and slowly pour in milk while whisking until fully combined.
Bring to a boil, whisking occasionally (about 10 minutes). Do not increase heat.
Once bubbling in the center, whisk constantly and boil for 1 minute until thickened.
Remove from heat and whisk in butter and vanilla.
Chill the Pudding
Pour pudding into a heatproof bowl and let sit for 5 minutes.
Place plastic wrap directly on the surface to prevent a skin.
Refrigerate for 1 hour (it should still be slightly soft for layering).
Prepare Oreo Crumbs
Pulse Oreo cookies in a food processor or blender until fine crumbs form.
Assemble the Dessert
Add a layer of Oreo crumbs to the bottom of each cup (a few tablespoons).
Spoon about 1/4 cup pudding over crumbs.
Add another layer of Oreo crumbs, followed by more pudding.
Finish with a top layer of Oreo crumbs.
Add gummy worms on top.
Chill and Serve
Refrigerate uncovered for at least 3 hours (up to 48 hours).
Serve chilled.
Do not rush pudding cooking; proper thickening requires steady heat.
Whole milk gives the best texture and richness.
Layer in clear cups for a more appealing presentation.
