With an electric mixer, cream butter and sugars in a small mixing bowl.
Add vanilla and egg; cream again until smooth.
Add the flour, baking soda, and salt.
Stir gently until incorporated.
Stir in chocolate chips.
Store in the refrigerator until ready to use.
Preheat the oven to 350 degrees.
Prepare brownie batter as directed.
Pour batter into a greased glass 9×13 baking dish ( or use parchment paper).
Scatter pieces of cookie dough over the top of the brownie batter.
Bake for 35-40 minutes or until you can insert a toothpick and it comes out clean. If you are covering with foil to keep the cookies from getting too brown on top, leave for 50 minutes or more and keep checking every 5 minutes until you can insert a toothpick and it comes out clean.
While baking take your Cadbury creme eggs and half them, then set aside.
Once out of the oven quickly place the Cadbury creme eggs on top and the pastel M&M’s.
Let stand for 15-20 minutes and cut into pieces for serving.