Preheat your oven to 350°F (175°C). Grease the 9-inch round cake pan and line the bottom with parchment paper.
In a double boiler, melt the bittersweet chocolate and unsalted butter together until smooth.
Whisk together the egg yolks and sugar until pale and creamy.
Gently fold the melted chocolate mixture into the egg yolk and sugar mixture.
Carefully fold in the super-fine almond flour until just combined.
Whip the egg whites in a separate bowl until stiff peaks form.
Gently fold the whipped egg whites into the chocolate mixture in three additions.
Pour the batter into the prepared cake pan and smooth the top. Bake for 30-35 minutes until set and slightly cracked on top.
Cool the cake in the pan for 15 minutes, then transfer to a wire rack to cool completely. Dust with powdered sugar before slicing and serving.