Line a 9x5x3 inch loaf pan with two pieces of plastic wrap at right angles, leaving 3 inches of overhang on each side.

Sift together cocoa and sugar.

In a stand mixer with a cold bowl and whisk attachment, whip cream and 7 tablespoons of the cocoa-sugar mixture until it holds firm peaks. Transfer to a bowl and refrigerate.

Wash mixer bowl and whisk attachment thoroughly.

Whip egg whips until frothy. Add cream of tartar and continue whipping. When whites hold soft peaks, add 1 tablespoon cocoa-sugar mixture and whip to combine. Add 1 additional tablespoon of cocoa-sugar mixture. Whip egg whites to firm peaks. Set aside.

Melt chocolate in microwave on 50% power.

In large bowl, whisk egg yolks, add remaining cocoa and sugar, and whisk until uniform in color. While whisking, pour in melted chocolate. Continue whisking until thickened and uniform.

In three additions, fold whipped cream into egg yolk mixture.

In three additions, fold in egg whites.

Scrape into pan, fold plastic around and freeze at least 8 hours, preferably overnight.

Slice to serve.