Crush the Oreos into fine crumbs using a large zip-top bag and a rolling pin, or a food processor.

Combine the crushed Oreos with milk in a mixing bowl, stirring until you achieve a smooth, thick, lump-free batter.

Lightly grease a microwave-safe mug for a single serving or an 8x8 inch baking dish for a larger cake.

Pour the batter into the prepared dish and microwave on high: 1-2 minutes for a mug cake, or 5-8 minutes for a larger cake, until a toothpick inserted into the center comes out clean.

Alternatively, preheat your oven to 350°F (175°C), pour the batter into an 8x8 inch greased baking dish, and bake for 20-30 minutes, or until a toothpick comes out clean.

Allow the cake to cool slightly before serving.