Preheat the oven to 325 degrees. Butter and flour six, 6 ounces custard cups.
Place chocolate and butter in a metal bowl and set it over a pan of simmering water. Stir until melted and smooth. Cool slightly.
Using an electric mixer, beat the eggs, yolks and sugar until they are pale and thick, about 10 minutes. Reduce the speed and gradually mix in the flour.
Add the chocolate mixture to the flour mixture and continue to beat until thick and glossy, about 5 minutes.
Divide among the prepared cups. Add 1 tablespoon. chopped chocolate. Bake until the cake is set around the edges but the center moves slightly when the cup is moved, about 12 minutes. Cool slightly.
Run a sharp knife around the edges of the cups. Turn out onto plates and serve with warm ice cream.