Cheesecake Swirl Walnut Brownies

Steps

1. Heat the oven to 350°F (175°C). Grease an 8-inch square pan lightly with a little of the butter and line it with parchment, leaving an overhang.
2. Spread the walnuts on a small tray and toast in the oven for 6–8 minutes until fragrant, then cool and chop.
3. Make the cheesecake layer first: beat the cream cheese with one quarter of the sugar until smooth, then beat in 1 of the eggs and one third of the vanilla. Set aside.
4. Make the brownie batter: melt the remaining butter with the chocolate chips in a heatproof bowl over barely simmering water (or in short microwave bursts), stirring until smooth. Let cool 5 minutes.
5. Whisk the remaining three quarters of the sugar into the chocolate mixture, then whisk in the remaining 2 eggs one at a time and the remaining two thirds of the vanilla until glossy.
6. In a small bowl, whisk together the unsweetened cocoa powder, the flour and the salt.
7. Sift the cocoa powder mixture over the chocolate batter and fold until just combined, then fold in the walnuts.
8. Spread about three quarters of the brownie batter in the pan. Dollop the cheesecake mixture over it, then dollop the remaining brownie batter on top. Drag a knife through both in loops to marble.
9. Bake 33–38 minutes, until the cheesecake swirls are set and lightly puffed and a toothpick in the brownie part comes out with a few moist crumbs but no wet batter; the cheesecake should reach 160°F (71°C).
10. Cool in the pan on a rack for 1 hour, then refrigerate at least 1 hour so the swirl firms up.
11. Lift out by the parchment and cut into 12 bars with a hot, wiped knife. Keep leftovers in the fridge.