9 tbsp. unsalted butter
6 tsp. flour
4 oz. bittersweet chocolate
2 egg yolks
1/4 cup sugar
1 tbsp. unsweetened cocoa
1. Preheat oven to 450°. Butter four 4-oz. molds, custard cups, or ramekins with 1 tbsp. of the butter. Dust each mold with 1 tsp. of the flour, tapping out excess, then put on a baking sheet.
2. Put chocolate and the remaining 8 tbsp. butter into the top of a double boiler set over a pan of simmering water over medium-low heat and heat until almost completely melted, about 10 minutes.
3. Meanwhile, beat eggs, egg yolks, and sugar together in a mixing bowl until thick and pale yellow, 2–3 minutes.
4. Whisk chocolate and butter together, then add to egg mixture, stirring until just combined. Whisk in the remaining 2 tsp. flour.
5. Divide batter between prepared molds and bake for 6–7 minutes (center of cakes will be very soft). Invert cakes onto 4 individual dessert plates and let rest, undisturbed, for about 10 seconds. Lift up an edge of each mold to let cake fall out onto plate. Dust cakes with cocoa and serve immediately, with a small scoop of vanilla or other ice cream, if you like.