Preheat the oven to 325°F (163°C). Grease a 9-inch springform pan and line the bottom with parchment. Wrap the outside of the pan with foil if using a water bath.

Bring cream cheese to room temperature.

In a medium saucepan over low heat, melt butter and chopped chocolate together, stirring until smooth. Remove from heat and let cool slightly.

Stir in granulated and brown sugars until combined. Add eggs one at a time, mixing well after each addition. Stir in vanilla.

Sift in flour, cocoa powder, and salt; fold until just combined.

Spread batter evenly into the prepared pan and bake for 12-15 minutes.

Remove from oven and let cool slightly.

Beat the room-temperature cream cheese with sugar until smooth and creamy.

Add eggs one at a time, mixing until blended. Stir in sour cream, vanilla, and optional flour.

Pour cheesecake filling over the partially baked brownie layer, smoothing the top.

Return the pan to the oven. If using a water bath, place the springform pan in a larger roasting pan and carefully pour hot water in until halfway up the springform sides.

Bake for 45-55 minutes, or until the cheesecake center is slightly jiggly.

In a medium saucepan over medium heat, melt sugar until it turns into an amber liquid.

Add butter, then slowly drizzle in warm cream while stirring. Let simmer until smooth.

When cheesecake is done, cool it on a wire rack for 30 minutes.

Spoon half of the caramel sauce over the cheesecake and swirl gently.

Cool completely at room temperature, then refrigerate for at least 4 hours, preferably overnight.

Run a thin knife around the springform edge before releasing. Drizzle with remaining caramel and sprinkle with sea salt flakes and chopped nuts.