Preheat oven to 325°F (165°C). Wrap the outside of a 9-inch springform pan with two layers of heavy-duty foil. Lightly grease the inside and press a parchment circle onto the base.
Mix crushed cookies and melted butter until the mixture holds when pressed. Press firmly into the base and ½ inch up the sides. Bake 10 minutes. Cool completely.
Combine chopped dark chocolate and heavy cream in a heatproof bowl over barely simmering water. Stir until smooth. Remove and cool for 10 minutes.
Beat cream cheese on medium speed for 2 minutes until smooth. Add sugar and cocoa; beat on medium-low until uniformly colored with no white streaks.
Add cooled chocolate to cream cheese batter and beat on low until just combined. Add eggs one at a time on the lowest speed — beat only until each disappears. Add vanilla. Stop mixing.
Pour filling over cooled crust. Smooth the top. Place the springform in a roasting pan; add hot water to 1 inch depth. Bake 60–70 minutes until edges are set and the center wobbles slightly.
Turn oven off. Crack door open 1 inch. Leave cheesecake in oven for 60 minutes. Remove from water bath, cool on rack for 60 minutes. Run a knife around the edge, cover, and refrigerate at least 6 hours before slicing.
