Preheat your oven to 350°. While the oven is preheating, rub 2 round baking pans with butter (9"x9" is the ideal size) and line them with parchment paper. Then rub butter on top of the paper and sprinkle with a little flour to prevent sticking
Follow the instructions of your pre-bought cake mix until it's ready to go into the oven. At this point, add the crushed Oreos until combined well. Divide the batter evenly among the pans you prepared earlier. Bake for around 25-30 minutes (if your box instructions are different, follow those). Once baked, leave to cool on a cooling rack
While your cake is cooling, you can start on the frosting. Beat the butter until it reaches a light and fluffy consistency. Now add the cookies and creme bars (remember to melt them first). Add the powdered sugar gradually, making sure it's combined well. Once the powdered sugar has been added, add the vanilla extract and milk. Beat until there are no lumps remaining
Put around 1/4 of the frosting mix onto one-half of the cake. Now put the second cake on top of your frosted cake. With the remaining frosting, coat the sides and top of your cake. Use Oreos to line the outside of your cake and add the crushed Oreos on top. You can go wild with the decoration - use as many Oreos as you'd like!Your cake is ready to serve!