HEAT oven to 425°F.
BUTTER 4 (3/4-cup) custard cups or ramekins. Place on baking sheet.
MICROWAVE chocolate and butter in large microwaveable bowl on HIGH 1 min. or until butter is melted. Stir with whisk until chocolate is completely melted. Add 1 cup sugar; mix well. Blend in whole eggs and egg yolks. Stir in flour. Pour into custard cups.