Start by crushing the Oreo cookies into fine crumbs using a food processor or by placing them in a zip-top bag and crushing with a rolling pin. Reserve 1/2 cup of the crumbs for later. In a large mixing bowl, combine the remaining crumbs with melted unsalted butter and mix until the texture resembles wet sand. Press this mixture firmly into the bottom of a 9x13-inch dish to form a sturdy crust.

In a clean mixing bowl, beat the softened cream cheese and melted unsalted butter together using an electric mixer on medium speed until smooth and creamy, about 2-3 minutes. Gradually add in the powdered sugar, ensuring there are no lumps, and mix until fully incorporated. Carefully fold in the thawed whipped topping.

In a separate bowl, whisk together the instant vanilla pudding mix and 2 cups of cold milk until it thickens—this should take about 2-3 minutes. Gently fold this pudding mixture into the cream cheese filling until smooth and uniform.

Spread the creamy filling evenly over the prepared Oreo crust in the dish, ensuring no crust is exposed. Sprinkle the reserved Oreo crumbs on top and decorate the pudding layer with mini Oreo cookies and colorful pastel candy-coated chocolates.

Cover the assembled Easter Dirt Cake Casserole and refrigerate for at least 2 hours, or overnight for best results.