Bring cream cheese, eggs, and sour cream to room temperature for 2 hours for a smooth cheesecake.

Preheat oven to 325°F and wrap a 9-inch springform pan in two layers of heavy-duty foil.

Process Oreos into fine crumbs, mix with melted butter, and press into the pan. Chill while preparing the filling.

Melt chocolate in 30-second bursts in the microwave, stirring until smooth. Let cool.

Beat cream cheese until smooth, then mix in sugar until fluffy. Add eggs one at a time, mixing gently.

Stir in melted chocolate, cocoa powder, sour cream, vanilla, and salt until combined. Scrape the bowl well.

Pour filling into the crust. Place the pan in a larger roasting pan and add hot water halfway up the sides.

Bake for 1 hour until edges are set and the center jiggles slightly.

Turn off the oven, crack the door, and cool for 1 hour inside.

Remove from the water bath, cool completely on a wire rack for 2 hours.

For ganache, heat cream until bubbling, pour over chopped chocolate, and stir until glossy.

Pour ganache over cheesecake and chill for at least 2 hours or overnight before serving.