Brownie batter

1. Chop the chocolate and butter in a bowl and melt in a double boiler over a saucepan containing a little water until the mixture is liquid and lump-free.
2. In another large bowl, place the eggs with the white sugar, brown sugar and vanilla extract and beat with an electric whisk for about 2 minutes until the mixture is thick and glossy.
3. Add the chocolate and melted butter and beat again with an electric mixer until smooth.
4. Add the dry ingredients, cocoa powder, flour and salt and mix with a rubber spatula until smooth.
5. Add the crushed Oreo cookies, and mix again to incorporate.
6. Pour the chocolate brownies batter into the bottom of a square pan lined with parchment paper, and smooth the surface with an angled spatula.

Cheesecake : 

1. Place all the ingredients, cream cheese, sugar, egg and vanilla extract in a medium bowl and mix with an electric mixer until smooth and liquid.
2. Pour the cheesecake mixture into the prepared pan over the brownie batter.
3. Use a knife to lightly swirl the top, then add Oreo cookie pieces for decoration.

Baking 

1. Preheat the oven to 350°F / 180°C and bake the cheesecake brownies for around 35 - 40 minutes, until lightly golden on top.
2. Leave to cool to room temperature before covering with plastic wrap and placing in the fridge for at least 1 hour before cutting into 16 equal slices.