Position rack in middle of oven and preheat to 450 degrees F. Butter and flour four 4-ounce ramekins.
STEP - 2
Melt chocolate with butter. Remove from heat. Beat eggs, yolks and sugar with an electric mixer on high speed in a deep bowl, 8 minutes, until thick and pale. Whisk chocolate mixture into egg mixture. Whisk in flour.
STEP - 3
Pour batter into ramekins. Place on baking sheet and bake 14 minutes, or until cakes have risen and have a thin crust, sides are set and cakes are slightly jiggly in the center; under baking is better than over baking.
STEP - 4
Carefully invert each cake onto a serving plate and let sit 20 seconds. Unmold by lifting up one corner of mold; cake will fall onto plate. Dust tops with confectioners' sugar and serve immediately.