Preheat the oven to 350F. Line baking sheets with parchment paper or silicone baking mats.
Beat butter and sugars together until well-combined, about 2-3 minutes.
Mix in the eggs one at a time, scraping down the bowl as needed.
Add vanilla extract, and mix to combine.
Add the cocoa powder, flour, salt and baking powder; mix until just incorporated.
Add the Oreo cookies to a food processor or blender and process until crumbs form.
Pour the crumbs into a shallow dish.
Scoop dough in 3 tablespoon scoops.
Roll each scoop of dough into a ball and then roll the cookie dough into the Oreo cookie crumbs.
Place on baking sheet about 2 inches apart.
Bake about 12 minutes. The cookie should be done at the edges but should look soft and slightly underdone in the centers.
Let cool on the baking sheets 5 minutes, and then transfer to a wire rack to cool completely.
Once the cookies have finished cooling, frost with chocolate buttercream frosting.
Top each cookie with a gummy worm.
Notes
Unsalted butter: You can use salted butter. Just reduce the salt to 1/4 teaspoon or omit the salt.
Brown sugar: I use light brown sugar.
All-purpose flour: To measure the flour either weigh it or sift/stir it to break it up. Lightly spoon into the measuring cup and level. Using too much flour will give you heavy or dry cookies.
Oreo cookies: I use either regular Oreo cookies or dark chocolate Oreo cookies.
Heavy cream: The cream works well to help give the frosting its creamy texture and taste.