Pre heat oven to 350°F.
Spray 9" round cake pan with a removable bottom with vegetable spray and dust with cocoa powder.
Chop chocolate into coarse pieces. Place chocolate and butter in a microwave proof dish and heat on high for 30 seconds, stir and heat for another 30 seconds, set aside to cool.
In a mixing bowl, mix the egg yolks and sugar and salt with a hand mixer at high speed for 3 - 5 minutes, or until the egg mixture has tripled in volume and is a pale yellow. Add the cocoa powder and mix well to combine.
Pour the cooled butter and chocolate mixture into the egg mixture and mix on low speed until completely blended.
In a separate bowl, whip egg whites until they form soft peaks, add the chocolate mixture and blend on low speed until fully combined.
Pour the batter into the prepared baking pan and bake for 35 - 40 minutes, or until just barely set in the middle.
Allow the torte to cool for at least 30 minutes then cover the cooled torte in its pan with aluminum foil and refrigerate for 4 hours or overnight.