While there are those who would argue that this combination of dense, fudgy, pudding-centered chocolate cake and rich chocolate sauce is too much of a good thing, they are few in number compared with those who will find this dessert enchanting. The cakes should be baked shortly before serving, but the batter may be prepared and placed in the molds before dinner starts.
5 egg yolks
Using an electric stand mixer, beat eggs, egg yolks, and sugar until the mixture is very pale and falls in flat ribbons from the lifted beaters.
While the eggs are being beaten, melt the chocolate and butter together in a double boiler over low heat or in a microwave at half power. Allow to cool slightly.
Butter 8 shallow, 4-ounce molds, sprinkle with sugar, and set aside. When egg-sugar mixture is ready, beat in the chocolate mixture, then carefully fold in the flour. Divide the batter among the molds and reserve. Unbaked cakes may be held for up to 4 or 5 hours; refrigerate if holding for longer than 1 hour.
Prepare chocolate sauce (below), and set aside.
About a half hour before serving, heat oven to 375 degrees F. Bake cakes for 10 minutes, 20 if they have been refrigerated. Allow to sit for about 5 minutes after they come from the oven, then unmold onto warmed dessert plates and serve with the sauce.