Preheat oven to 350 degrees F. Butter 12 (4-ounce) ramekins. Melt chocolate and butter in double boiler, stirring gently. Add sugar. Remove from heat and keep warm.
In a large bowl beat eggs and yolks until volume is doubled. Fold in flour gently until well incorporated. Fold 1/4 of warm chocolate mixture with egg mixture, to temper. Combine mixtures by folding gently. Fill ramekins 2/3 full. Bake for 4 to 6 minutes.