Preheat the oven to 325°F (160°C). Wrap a 9-inch springform pan with two layers of heavy-duty foil.
Pulse the Oreo cookies into fine crumbs. Mix with the melted butter until evenly coated, then firmly press into the bottom of the prepared pan.
Bake the crust for 10 minutes and let it cool.
Melt the dark chocolate until smooth and allow it to cool slightly.
Beat the cream cheese and sugar until smooth. Mix in the cocoa paste (made by whisking the cocoa powder with hot water), melted chocolate, and sour cream.
Add the eggs one at a time, mixing on low speed just until combined.
Pour the batter over the cooled crust and smooth the top.
Place the springform pan into a roasting pan and carefully pour boiling water into the roasting pan until it reaches halfway up the sides.
Bake for 60–70 minutes, until the edges are set and the center still jiggles slightly.
Turn off the oven, crack the door open, and let the cheesecake cool inside for 1 hour.
Remove from the water bath and refrigerate for at least 6 hours, preferably overnight.
For the topping, cook the cherries with the sugar and lemon juice until softened. Stir in the cornstarch slurry and simmer until thickened. Cool completely.
Whip the heavy cream with the powdered sugar until soft peaks form. Spoon the cherry topping over the chilled cheesecake, decorate with whipped cream and chocolate shavings, then serve.