For B's birthday, I made the "Rich Chocolate Cake" from Chez Panisse Desserts. Except for the pictures at the end, the rest of this post is unapologetic plagiarism, formatting (as best as I can reproduce it) and all.
Makes one 8-inch or 9-inch cake: 1 cup plus 2 tablespoons salted butter • 7 ounces semisweet chocolate • 2 ounces bitter chocolate • 6 eggs • ¾ cup granulated sugar • 3⁄8 cup brown sugar • 3⁄8 cup cake flour • 3 tablespoons finely grated almonds • ½ teaspoon cream of tartar
The flavor of this cake depends almost completely on the chocolate, so be sure to use the best semisweet chocolate you can buy.
Butter the sides and bottom of an 8-inch or 9-inch springform pan. Line the bottom with baking parchment or waxed paper and flour the pan. Melt the butter in a large heavy-bottomed pan. Chop the chocolate in coarse pieces and add to the butter. Stir constantly over low heat until just melted and smooth; be careful not to overheat or the chocolate will turn grainy. It should not get much hotter than 115°F. Set aside.
Separate the eggs and beat the sugars into the egg yolks until just mixed. Which the chocolate is still warm, which the egg mixture into it, then stir in the flour and the almonds. If the combined mixture has cooled, warm if over low heat, stirring constantly, until it is barely warm. Warm the egg whites slightly by swirling them in a bowl above a gas flame or over hot water—the whites will beat to a greater volume when warmed. Add the cream of tartar to the egg whites and beat until they look creamy and form rounded peaks: if they look at all flaky they are overbeaten. Spread the egg whites over the chocolate mixture and fold them together quickly without deflating the whites. Pour into the prepared pan and bake in a preheated 375°F oven for 30 to 40 minutes, or until the cake is completely set around the sides but still has a soft creamy circle, about 6 inches across, in the center. The cake will rise and crack around the edge and separate from the softer center. The center should wiggle just slightly when you shake the pan gently; it will continue to cook when you take it out of the oven. Cool thoroughly in the pan.
To serve the cake, turn it out, peel the paper off the bottom, and ice with chocolate icing or powder lightly with vanilla powdered sugar. The cake keeps very well, if not iced, for three or four days. Do not refrigerate or freeze, just cover the pan with foil until ready to use.
This is a synthesis of a number of French recipes for gâteau au chocolat. The cake is very good with Rum, Cognac, or Vanilla Ice Cream, or it can be served with crème Chantilly. Coffee, of course, is welcome afterward.