Preheat oven to 350° F. Butter and flour 8-inch round cake pan. Set aside.
Set chocolate and rum or coffee in a small pan, cover, and place (off heat) in a larger pan of almost simmering water; let melt while you proceed with the recipe. Measure out the rest of the ingredients.
Cream the butter and sugar together for several minutes until they form a pale yellow, fluffy mixture. Beat in the egg yolks until well blended.
Beat the egg whites, salt and cream of tartar in a separate bowl until soft peaks are formed; sprinkle on 2 Tablespoons of sugar and beat until stiff peaks are formed.
With a rubber spatula, blend the melted chocolate into the butter and sugar mixture; then stir in the almonds and almond extract. Immediately, stir in one fourth of the beaten egg whites to lighten the batter. Delicately fold in a third of the remaining whites and when partially blended, sift on one third of the flour and continue folding. Alternate rapidly with more egg whites and more flour until all egg whites and flour are incorporated.
Turn the batter into the cake pan, pushing the batter up to its rim with a rubber spatula. Bake in middle level of preheated oven for about 25 minutes. Cake is done when it has puffed, and 2-1/2 to 3 inches around the circumference are set so that a needle plunged into that area comes out clean; the center should move slightly if the pan is shaken, and a needle comes out oily.
Allow cake to cool in the pan for 10 minutes. Run a knife around the edge of the pan, and reverse cake on the rack. Allow it to cool an hour or two; it must be thoroughly cold if it is to be iced. Ice with chocolate-butter icing. Yield: Serves 6 to 8 people.
Glaçage au Chocolate (Chocolate-butter Icing from page 684 of Mastering the Art of French Cooking, Volume 1): 2 ounces semi-sweet chocolate; 2 Tablespoons rum or coffee; 6 Tablespoons unsalted butter, room temperature. Place the chocolate and rum or coffee in a small pan; cover and set in a larger pan of almost simmering water. Remove pans from heat and let chocolate melt for 5 minutes or so, until perfectly smooth. Lift chocolate pan out of the hot water, and beat in the butter, a tablespoon at a time. Then beat over ice and water until chocolate mixture has cooled to spreading consistency. At once, spread it over your cake with spatula or knife.