Preheat the oven to 180c. Lightly grease a circular 9" loose bottomed/spring form tin.
Crush the digestive biscuits to a fine crumb and pour in the melted butter. Mix together then press into the tin. Press down and all the way to the edges, ensuring an even layer.
Make the brownie part: Combine the melted butter and sugar in a large bowl using an electric mixer. Add in the eggs and vanilla and mix until combined.
Fold in the flour and cocoa powder. Reserve about 1/4 cup (a small scoop) of the brownie batter and set aside. Pour all remaining batter over the biscuit base.
Make the cheesecake topping by combining all ingredients with a whisk. Pour this over the brownie.
With that reserved brownie mixture, add about 1 tbsp water and mix to thin. Pour over the cheesecake in lines then feather by using a knife - drag it through the top of the mix in up and down motions.
Bake for 35-40 minutes, until the edges have browned slightly and the centre stops wobbling. Let cool, then slice and serve!