Grease the sides of a 2-quart souffle dish with butter or margarine. For a collar on the souffle dish, measure enough foil to wrap around the top of the souffle dish and add 3 inches. Fold the foil in thirds lengthwise. Lightly grease one side with butter or margarine; sprinkle with sugar. Attach the foil, sugar side in, around the outside of the dish so that the foil extends about 2 inches above the dish. Tape ends of foil together. Sprinkle sides of dish with sugar. Set the dish aside.
Melt chocolate in a small saucepan over low heat, stirring constantly. Set aside.
Melt 3 tablespoons butter or margarine in a medium saucepan. Stir in flour. Add half-and-half, light cream, or milk all at once. Cook and stir over medium heat until mixture is thickened and bubbly. Remove from heat. Stir half of the hot cream mixture into the chocolate; set aside.
Stir peanut butter into the remaining hot cream mixture in the saucepan. Beat 2 of the egg yolks in a medium mixing bowl just until combined. Gradually stir the peanut butter mixture into the beaten yolks; set aside.
Beat the remaining egg yolks in another bowl. Gradually stir the chocolate mixture into the remaining egg yolks; set aside.
In a large mixing bowl, using clean beaters, beat egg whites with an electric mixer on medium to high speed until soft peaks form (tips curl). Gradually add 1/3 cup sugar, about 1 tablespoon at a time, beating until stiff peaks form (tips stand straight) and sugar is completely dissolved.
Gently fold half of the beaten egg white mixture into the peanut butter mixture. Transfer peanut butter mixture to the prepared souffle dish. Gently fold the remaining egg white mixture into the chocolate mixture. Spoon chocolate mixture on top of peanut butter mixture in the souffle dish. Using a small narrow metal spatula, gently swirl the chocolate mixture into the peanut butter mixture.
Bake in the preheated oven for 45 to 50 minutes or until a knife inserted near the center comes out clean. Serve at once. Makes 6 to 8 servings.