Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 9-inch springform pan.

To make the crust: Mix 1 ½ cups chocolate wafer crumbs, melted butter, and 2 tablespoons sugar together in a small bowl until well combined; press onto the bottom and 1 ½ inches up the sides of the prepared pan. Bake in the preheated oven for 10 minutes; allow to cool. Reduce oven temperature to 325 degrees F (165 degrees C).

To make the filling: Heat ¼ cup whipping cream and ¼ cup chocolate chips in a small saucepan, stirring constantly, until chips are melted. Remove from heat and set aside.

Beat cream cheese and 1 cup of sugar with an electric mixer in a large bowl until smooth. Add cocoa and beat well. Add eggs and beat on low until just blended. Stir in 1 teaspoon vanilla and melted chocolate-cream mixture until blended; pour filling over crust.

Bake cheesecake in the preheated oven until edges are puffed and surface of cheesecake is firm except for a small spot in the center that will jiggle when the pan is gently shaken, about 45 to 50 minutes. Run the tip of a table knife around the edges of the pan, set the pan on a wire rack, and allow the cheesecake to cool at room temperature.

To make the chocolate topping: Place 1 ½ cups chocolate chips in a medium bowl. Heat ¼ cup whipping cream and 1 teaspoon vanilla in a small saucepan, stirring continuously, until just before boiling; pour hot cream over chocolate chips and stir with a spoon until smooth. Spread over baked cheesecake and refrigerate for at least 4 hours to overnight.