Pre-heat oven to 350°F / 180°C and line a 9-inch square pan with parchment. Room-temperature eggs and sugar whisked into custard-like consistency in large bowl. An electric mixer, handheld whisk, or stand mixer with the whisk attachment can do this. Fudgy brownies require pale, thick batter.
2
Break the chocolate into small pieces in a heatproof bowl, then add the butter and microwave in 30-second increments, stirring until melted and lump-free.
3
Pour the melted chocolate/butter mixture into the whipped egg/sugar mixture and whisk until combined. Add flour and salt to brownie batter and gently fold in until all flour is incorporated.
4
We'll swirl half a cup of brownie batter into the cheesecake later. Spread the remaining brownie batter evenly in the prepared pan. Set aside while making cheesecake.
5
Set the oven to 45 minutes. You can tell it's done because the edges should be turning a little golden and the middle should still be able to wobble a little.
6
Combine all cheesecake ingredients in a medium bowl and beat until smooth. To avoid lumps in the cheesecake topping, use room-temperature cream cheese and eggs and sieve the powdered sugar.
7
Use butter knife to'meld' smooth cheesecake mixture into brownie batter. To avoid layer separation during baking, lightly mix. Spoon small dollops of reserved brownie batter onto cream cheese mixture and swirl with tooth pick or knife to make patterns.