Line a 9x9 inch square baking pan with parchment paper.

To make the cookie dough layer beat the butter and sugar until it is light and fluffy. Add the egg and vanilla extract and beat again until smooth.

Add the flour and baking soda, mix until combined.

Add the chocolate chips, fold into the cookie dough.

Transfer the cookie dough into prepared baking pan. Use your hands to press it down into an even layer. Put the pan into the freezer for 20 minutes.

Preheat the oven to 350ºF.

To make the brownie layer, melt the butter and the chocolate in 30 second bursts in the microwave, stirring well each time. It will take approximately 1-2 minutes.

Add the eggs and sugars into a large mixing bowl and whisk them until they are thick and frothy.

Pour the melted chocolate, butter mixture and vanilla extract into the bowl while stirring. Stir until combined.

Add the flour, salt and cocoa powder. Fold into the mixture gently taking care not to over mix.

Take the cold cookie layer out of the freezer. Arrange 16 Oreos on top of the cookie base then pour over the brownie mixture. Use a spatula to spread out the brownie batter into an even layer.

Sprinkle the chopped Oreos and chocolate chips over the top.

Bake in the center of the preheated oven for 35-40 minutes or until a toothpick inserted into the middle comes out mostly clean.

Allow to cool in the pan for a couple of hours before removing and slicing into 16 equal squares.

Serve as is or with vanilla ice cream and a drizzle of melted chocolate.