Peanut Butter Pudding Whisk sugar, cornstarch, and salt in saucepan. Gradually whisk in milk and cream. Over medium heat, cook whisking constantly, until it comes to a boil and large bubbles pop at the surface. Boil until thick, whisking constantly, about 30 seconds. Whisk in peanut butter and boil until thick again, whisking often, about 1 more minute. Remove from heat and whisk in vanilla. Divide pudding (1/3 cup each) into 6 1-cup glasses. Chill uncovered.

Chocolate Pudding Whisk sugar, cornstarch, cocoa powder and salt in saucepan. Gradually whisk in milk and cream. Over medium heat, cook pudding, whisking constantly, until it comes to a boil and large bubbles pop at the surface. Boil until thick, whisking constantly, about 30 seconds. Stir in chopped chocolate. Boil until chocolate melts and pudding is thick again, whisking 1-2 minutes longer. Remove from heat and whisk in vanilla. Cool 10 minutes. Spoon a heaping 1/3 cup chocolate pudding on top of  chilled peanut butter pudding. Chill cups uncovered until cold, at least 2 hours.

Whipped Cream Topping Beat cream and powdered sugar in a medium bowl with an electric mixer to soft peaks. Spoon topping onto puddings, dust with cocoa powder, if desired, and serve immediately.