Preheat oven to 350°. Prepare a 9 inch springform pan by lightly buttering the bottom and sides. Line bottom with parchment paper.
Combine eggs, sugar, and salt in a stand-mixer. Beat on medium high speed until mixture is pale and thickens. About 6-8 minutes.
While the eggs and sugar mix, combine the chocolate and 1½ sticks of butter in a heat-proof bowl. Place bowl over simmering water on the stove-top. Stir until melted.
Add cocoa powder and tahini into the heated chocolate and stir until combined.
Remove from heat and gently fold half of the chocolate mixture into the egg mixture. Once just combined, add the remaining chocolate mixture and fold in gently until combined.
Pour batter into prepared pan and bake 35-40 minutes.
Cake is finished when a toothpick inserted into the center comes out with only a few crumbs. Cake will no longer jiggle.
Transfer pan to a wire rack to allow to cool completely. Remove from pan prior to serving, transfer to platter and dust with dark cocoa.
