Preheat oven to 350°F (175°C). Grease a 9-inch springform pan.
Mix chocolate cookie crumbs, melted butter, and 2 tablespoons sugar. Press into the pan. Bake for 10 minutes, then cool. Reduce oven temperature to 325°F (165°C).
Heat 1/4 cup whipping cream and 1/4 cup chocolate chips in a saucepan until melted. Set aside.
Beat cream cheese and 1 cup sugar with an electric mixer until smooth. Add cocoa and beat. Add eggs, vanilla, and chocolate-cream mixture. Blend well and pour over the crust.
Bake for 45-50 minutes until edges puff and center jiggles slightly. Run a knife around the edges. Cool on a wire rack.
For the topping, heat 1/4 cup whipping cream and 1 teaspoon vanilla until near boiling. Pour over 1 1/2 cups chocolate chips in a medium bowl and stir until smooth. Spread over cheesecake.