Preheat the oven to 350 degrees. In a large bowl, beat the sugar and egg with an electric mixer, until creamy. Add the cream cheese and beat until well incorporated. Beat in the ricotta cheese. Stir in the chocolate chips.
Pour the cheese mixture into the pie crust. Bake for 30 minutes, until the center doesn't jiggle when the pan is moved. Remove from the oven and coll to room temperature before serving. Dust the top with cocoa powder to cover lightly.