1. Heat oven to 425°F Butter 4 (3/4-cup) custard cups or soufflé dishes and place on baking sheet. 2. Microwave chocolate and butter in large microwaveable bowl on HIGH 1 minute or until butter is melted. Stir with whisk until chocolate is completely melted. 3. Add sugar; mix well. Blend in whole eggs and egg yolks. Stir in flour. 4. Pour 1/2 the batter evenly into prepared cups. Spoon 1 tablespoons peanut butter into centre of batter in each cup. Cover with remaining batter. 5. Bake 14 minutes or until sides are firm but centers are still soft. Let stand 1 minute. Carefully run small knife around edges of cakes to loosen. 6. Invert cakes onto dessert plates. Cut in half to serve.
