Pour milk and orange extract into large bowl. Add pudding mix. Beat with wire whisk until well blended. Stir in ricotta and 1/2 of the chocolate.
Spread 1/3 of the pudding mixture onto bottom slice of cake. Repeat layers twice, ending with top cake slice.
Microwave remaining chocolate in small microwavable bowl on high 45 seconds to 1 minute or until almost melted; stir until completely melted. Stir in whipped topping. Spread evenly over top and sides of cake.