Chop dark chocolate and dice unsalted butter
Sift cocoa powder and set aside
Separate eggs into yolks and whites
Combine chocolate, butter, cocoa powder and sea salt
Mix egg yolks with caster sugar
Combine chocolate mixture with egg yolk mixture
Fold in sifted potato starch and cornflour
Whip egg whites with cream of tartar until stiff peaks form
Gently fold egg whites into chocolate batter
Pour into prepared pan and bake for approximately 20 minutes until set but still moist
