This is an improvisation on a cake from my Gourmet cookbook -- I use a bit less sugar, for a richer flavor, and beat the egg whites for much better structure, IMHO. This is wonderful for dinner parties, a quickie hostess gift and children adore it. For the latter group, I like to cut out a shape (recently I used a trumpet for a Music Man cast party), lay it in the center of the cake held down with dimes, then sift powdered sugar over it. Carefully remove the paper pattern, and voilà, a themed cake. You can half this recipe and make in an 8 inch cake pan for smaller groups. —Jestei
Put rack in middle of oven and preheat to 350. Generously butter 10 inch spring form pan. Line bottom with parchment paper and butter paper.
Chop chocolate in small pieces and melt with butter over very low flame, stirring frequently until smooth. (You can also do this in microwave.) Remove from heat and whisk in sugar. Let cool for 5 minutes, then add egg yolks, one at a time. Sift cocoa and salt over chocolate mixture and whisk to combine.
In standing mixer, beat egg white at high speed until peaks form but are not yet stiff. Gently fold into chocolate mixture.
Pour batter into pan and bake 35-40 min or until cake forms thin crust on top. Remove before its sides move from pan.
Cool for ten minutes, invert on a plate then reinvert on cooling rack. (I have also served this right from cake pan, sides removed. Sue me.)
Let cool completely before sifting powdered sugar over top.