Combine crushed chocolate cookies with melted unsalted butter, pressing firmly into the bottom of a 9-inch springform pan. Chill for about 15 minutes.

Blend mascarpone cheese and cream cheese together until smooth. Gradually add powdered sugar, vanilla extract, and pinch of salt. Mix until velvety, about 2-3 minutes.

Melt dark chocolate in a microwave-safe bowl in 30-second intervals until smooth. Cool slightly, then fold into cheese mixture until uniform.

Whip heavy cream until stiff peaks form, then gently fold into the chocolate filling to incorporate until fully combined.

Pour the filling over the chilled crust, smoothing the top and tapping the pan to release air bubbles.

Preheat oven to 325°F (160°C) and bake for approximately 55 minutes until edges are set but center jiggles slightly.

Cool at room temperature for 1 hour, then refrigerate for at least 6 hours or overnight.

For optional ganache, melt additional dark chocolate with heavy cream, stir until smooth, then pour over the chilled cheesecake.