1. Line a brownie tin 22x29cm, 8 ½" x 11" with baking parchment. Heat your oven to 170°C.
2. Break 225g of chocolate into small chunks and place in a heatproof bowl with the butter. Place over a pan of simmering water and heat until melted. Leave to cool.
3. Beat the eggs and sugar together until pale and the mixture has thickened. Add the melted chocolate and butter mixture to the eggs and stir until thoroughly combined. Fold in the flour, salt, chocolate chunks and vanilla extract. Pour into the prepared in.
4. Using an electric whisk on a slow speed, beat the cream cheese with the custard powder, sugar, vanilla extract and cream. Mix until smooth and all the ingredients are combine.
5. Drop spoonfuls of cheesecake mix onto the brownie then using a spatula fold through the brownie to create swirls. Bake for 25-30minutes. Check after this time as ovens vary, it may need a little longer. A little mixture should still stick to a skewer when inserted in the middle of the brownie.
6. Leave to cool completely before cutting into squares.