Preheat oven to 425 degrees. Butter (or spray) four custard cups (3/4 cup) or souffle dishes. Put these cups/dishes on a cookie sheet.
Microwave your chocolate and butter in a large bowl for one minute (on high), or until your butter is completely melted. Stir this mixture with a wire wisk until the chocolate is completely melted.
Stir in sugar until well blended.
Wisk in eggs and egg yolks.
Stir in flour.
Divide batter between your four cups/dishes.
Bake for 13 - 14 minutes. You'll want the sides of the cakes to be firm, but the centers to be soft. After taking them out of the oven, let them stand for one minute.
Carefully run a thin knife around the cakes to loosen them from the cups.
Invert the cakes onto dessert plates, and serve immediately (topped with whip cream).