Preheat oven to 350 degrees.
Butter a 10 inch spring form pan and line
bottom with parchment 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