Microwave chocolate and butter in large microwaveable bowl on high for 1 minute or until butter is melted. Stir with wire whisk until chocolate is completely melted.
Stir in powdered sugar until well blended.
Blend in eggs and egg yolks with wire whisk.
Stir in flour.
Divide batter between prepared custard cups.
Bake 10-12 minutes or until sides are firm but centers are soft.
Remove from oven and let stand 1 minutes.
Carefully run small knife around cakes to loosen. Invert cakes onto dessert dishes. Serve immediately, topped with whipped cream.