Preheat oven to 350º F. Butter a 6-inch diameter springform pan with 3-inch high sides. Wrap the outside of the pan with foil, taking care not to tear the foil. Set aside.

Combine cookie crumbs with sugar and salt. Add melted butter and mix until well blended. Firmly press the mixture in an even layer across the bottom of the prepared pan. Bake until just set, about 8 minutes. Cool while preparing the filling. Maintain heat in oven.

Stir chocolate in a metal bowl set over simmering water until melted and smooth. Remove bowl from water and set aside to cool slightly.

Bring a large kettle of water to boil and place a roasting pan in the oven. Check the that the foil on the springform pan has no holes or gaps; if needed, add an extra layer of foil to prevent water from entering the pan during baking.

Beat cream cheese in the bowl of a standing electric mixture until smooth. Add sugar and cocoa powder and mix until well combined, scraping up from the bottom of the bowl with a spatula to ensure even mixing. Blend in eggs one at a time. Mix in melted chocolate.

Top prepared crust with the filling and smooth the top. Tap the pan on the counter gently a few times to release bubbles in the filling.

Place the cheesecake in the roasting pan and pour boiling water about ¾ of the way up the outside of the springform pan. Bake until the filling is set and just barely jiggles in the center, about 70 to 80 minutes. Remove cheesecake from the water bath, discard foil, and cool completely on a rack.

Once cool, refrigerate the cheesecake in the pan for at least two hours.

Place chopped chocolate for the ganache in a 1-cup heatproof glass measuring cup with a pour spout. Heat cream in a small saucepan until just simmering. Pour cream over the chocolate and let it sit undisturbed for 2 minutes. Mix with a small spatula until smooth and glossy. Let the mixture cool for a minute or two before pouring it over the center of the cheesecake. Chill until the topping is set, about 1 hour. If preparing ahead, cover pan with foil and keep refrigerated for up to three days.

To unmold, run a thin spatula around the edge of the chocolate ganache to separate it from the sides of the pan. Release pan sides. If needed, warm a long thin spatula and use the edge to smooth the ganache. Let stand at room temperature for an hour or two before serving.