From cooking school at the Ritz Paris.

5.5 oz. (170g) bittersweet chocolate
5 oz. (150g) butter
3/4 cup (160g) sugar
2.5 oz. (75g) flour
4 eggs

Butter and sugar the insides of six small ramekins, or use six small pastry rings lined with buttered/sugared parchment paper. Place on baking tray.

Melt chocolate and butter together.
Beat eggs and sugar together. Add chocolate/butter mixture and continue to beat five minutes.
Add flour and beat another two minutes.
Pour mixture into ramekins or pastry rings.
Bake in a 325 degree oven approximately 8-10 minutes.
Dust with powdered sugar and serve warm.