Preheat the oven to 220°C (430°F).
Crumble the chocolate and melt it in a double-boiler or microwave oven. When completely melted, remove from the heat and when still warm add the softened butter in pieces, blending to the chocolate with a whip.
Break the eggs and put the whites and yolks in two different bowls. Add the sugar to the yolks and beat with an electric eggbeater until the mixture is puffy, frothy and whitish. Continuing to use the beater, add the sifted flour and cocoa and the butter and chocolate mixture. Wash and dry the eggbeater, beat the whites until stiff and delicately fold in by hand. Pour the mixture into six well-greased muffin tins and bake for exactly 8 minutes.
Remove from the oven and wait two minutes before turning them out on dessert plates. Serve hot, if desired on a very cold crème anglaise flavored with vanilla or Cointreau; they are also excellent plain or served on a coulis of strawberries or raspberries.
The high heat of the oven will make the muffins immediately form a hard outer crust while the insides remain soft and creamy, which is why they need to be baked. You can prepare the batter ahead of time, storing the filled muffin tins in the refrigerator until you wish to bake them.
Chocolate lovers can enhance this dish by choosing between the two Donnafugata icon wines. Ben Ryé, the Passito di Pantelleria, one of the most appreciated Italian sweet wines in the world; Mille e una Notte, for those who prefer to taste chocolate with a structured and enveloping red that amazes with the great finesse of its tannins.