Combine the cake mix, milk, oil and egg in a large bowl. Beat with a mixer for 2 minutes, and then fold in chocolate chips. Line a 9×9″ pan with non-stick foil and pour the batter inside. The batter will be thick, so you may need to press it down.
Then gently cut the Cadbury Eggs in half. Then place the halves on top of the brownie mixture. You may need to make a little divot with a spoon to set the eggs in.
Bake for 18 to 20 minutes, or until a toothpick comes clean. Do not overcook. Let sit on the counter for one hour before cutting.