Mix graham cracker crumbs with melted butter and sugar; press crumb mixture into the bottom and 1/2-inch up the sides of an 8-inch springform pan. Refrigerate crust while making the filling.

Melt chocolate in the microwave on high power for 1 to 2 minutes, stirring every 15 seconds, until melted. Set aside to cool.

Whisk cocoa powder and enough hot water together in a medium bowl to form a smooth paste.

Beat cream cheese and remaining sugar into the cocoa mixture until combined.

In a chilled glass or metal bowl, beat heavy cream with an electric mixer until soft peaks form. Fold in cooled melted chocolate.

Fold the chocolate cream mixture into cream cheese mixture until thoroughly combined. Spread filling on top of the graham cracker crust.