Preheat the oven to 350°F / 180°C (or 170° fan-assisted) and line a 9-inch square baking pan with parchment paper.
Prepare the Brownie Batter
Whip the eggs and sugar together until the mixture becomes light and thick, similar to custard.
3 Eggs, 1 ¼ cups Granulated Sugar
Melt the butter and chocolate together in the microwave, heating in 30-second intervals.
1 ½ sticks Unsalted Butter, 10.5 oz Dark Chocolate
Add the melted chocolate and butter mixture into the egg and sugar mixture, stirring until fully combined.
Fold in the flour and salt until the mixture is smooth.
1 cup All-purpose Flour, ½ teaspoon Salt
Set aside a small portion of the brownie batter (about ⅓ cup, or more if you prefer more brownie on top), then pour the remaining batter into the prepared pan.
Make the Cheesecake Layer
Combine all cheesecake ingredients in a bowl and beat together until smooth.
13 oz Cream Cheese, 1 ½ cups Powdered Sugar, 1 teaspoon Vanilla Extract, 2 Eggs
Pour the cheesecake mixture on top of the brownie batter. Add dollops of the reserved brownie batter on top and swirl it into the cheesecake layer using a knife or spoon to create a marbled effect.
Bake
Bake for 30 to 35 minutes or until the edges of the cheesecake start to turn golden. There should still be a slight wobble in the center of the cheesecake. For gooey brownies, bake for the minimum time; for firmer brownies, extend the baking time a few minutes longer.
Allow the brownies to cool completely before slicing—this step is crucial!
