Whisk sugar, cocoa powder, cornstarch, and salt together in a medium saucepan and place the saucepan over medium heat. While whisking, slowly pour in the milk and whisk until combined.

Bring the mixture to a boil, whisking occasionally. This will take about 10 minutes and do not try to rush it by turning up the heat, as the pudding will not thicken properly. The mixture will begin to bubble around the edges, and then in the center. Once bubbling in the center, whisk constantly and allow to boil for 1 minute. The pudding should be thickened, and you’ll know it’s thickened enough if it coats the back of a spoon or spatula without dripping off.

Remove from heat, and then whisk in the butter and vanilla.

Pour into a heatproof bowl, let sit for 5 minutes, and then place a piece of plastic wrap directly on the surface of the pudding to prevent a skin from forming on top. Refrigerate for 1 hour. The pudding will not be fully thickened at this point, as you still want it a little thin to assemble the pudding cups in step 6.

Place the Oreos in a food processor or blender and pulse into crumbs.

It’s helpful to know that this recipe makes 4 cups of chocolate pudding, and you can make individual cups, a trifle, or assemble/serve in a 9-inch baking pan. The amount of pudding/Oreo crumbs in each cup really depends on the size of the cup (or other vessel) you are using. You’ll want to layer Oreo crumbs on the bottom, then pudding, Oreo crumbs in the middle, more pudding, and more Oreo crumbs on top. Start with a couple Tablespoons of Oreo crumbs in the bottom of each cup. Spoon 1/4 cup of pudding on top of the Oreo layer, then repeat with another couple of spoonfuls of Oreo crumbs, another 1/4 cup of pudding, and a final layer of Oreo crumbs. Place a few gummy worms in the top layer of Oreo crumbs.

Refrigerate uncovered for 3 more hours and up to 48 hours.

Cover and store leftover cups in the refrigerator for up to 3 days.