Heat oven to 350°F. Wrap a 9-inch springform pan base with foil, then grease and line the bottom with parchment.
Whisk melted butter, sugar, cocoa, espresso powder, and salt until glossy.
Beat in the beaten eggs and vanilla. Fold in flour just until no dry spots remain.
Spread brownie batter in the pan. Bake 12–15 minutes until edges look set. Reduce oven to 325°F.
Beat cream cheese until creamy. Mix in sugar and cornstarch until smooth and no lumps remain.
Blend in sour cream, vanilla, and salt. On low speed, slowly mix in the beaten eggs just to combine.
Pour cheesecake batter over the warm brownie base and smooth the top. Tap the pan to release bubbles.
Set the pan in a larger roasting pan. Pour hot water around it, reaching halfway up the sides.
Bake at 325°F for 45–55 minutes, until edges are set and the center jiggles slightly.
Turn off the oven, crack the door, and let the cheesecake rest inside 45–60 minutes.
Remove from the water bath. Run a thin knife around the edge. Cool to room temperature, then chill 4 hours or overnight.
Warm the cream until steaming. Pour over chocolate chips with a pinch of salt and let sit 2 minutes, then stir smooth.
Spread ganache over the chilled cheesecake. Chill 15 minutes to set, slice with a warm knife, and serve.