Preheat your oven: First things first, get your oven heating up to 350°f / 180°c. Then, get your 9” square pan ready by greasing it and lining it with parchment paper.
Melt the chocolate and butter: In a microwave-safe bowl, melt your dark chocolate and unsalted butter together. Heat in 30-second bursts, stirring in between, until it’s nice and smooth.
Bloom the cocoa: Sift Dutch process cocoa powder over the melted chocolate mixture and stir it all together until it's well mixed. This makes the chocolate taste extra rich!
Whip the eggs and sugar: In a big bowl, whip together the large eggs, caster sugar, and light or dark brown sugar with an electric mixer. Mix for 2-3 minutes until it looks light and fluffy.
Combine the wet ingredients: Pour the chocolate mixture into your fluffy eggs and mix it all up. Then, stir in the salt and vanilla extract.
Add the flour: Gently fold in all-purpose flour with a spatula until you don’t see any more flour streaks. Pour this delicious batter into your prepared pan and spread it out.
Make the cheesecake layer: In another bowl, whisk together all the ingredients for the cheesecake layer until it's completely smooth and has no lumps.
Swirl and bake: Drop spoonfuls of the cheesecake mix on top of the brownie batter. Use a toothpick to make pretty swirls! Bake for 22 to 28 minutes, or until just set.
