Preheat your oven to 350 F, or 180 C, and line your pan with buttered parchment paper.
In a double-boiler or a metal bowl set over a pan of simmering water, melt your chocolate. As it begins to soften, add the (optional) liquor, stirring gently until completely melted. Add the butter, and stir until everything is evenly melted.
Combine the dry ingredients. I like to use a whisk to mix in all together and break down any clumps.
Beat the egg whites until stiff.
Remove the chocolate mixture from the heat, and stir in the egg yolks. Fold the chocolate into the egg whites, gently.
Add the dry ingredients into the batter, about a third at a time, and then stir very gently to combine– do not over-mix.
Pour the batter into the cake pan and bake for 50 minutes, until the middle is semi-firm and an inserted knife blade comes out cleanly.
Allow to cool, then dust with cocoa powder and serve.
Keywords: Chocolate, hazelnut, grainfree, glutenfree, dark chocolate, flourless, cake