1. Preheat the oven to 350°F (180°C). Line a 9 inches (23cm) springform tin with baking parchment – bottom and sides. Works best if you grease the tin lightly before. Set aside.

2. Chop the chocolate and add together with the butter to a large heatproof bowl. Place that bowl over a pot with simmering water and melt. Mix until smooth. Take off the heat and let cool down a bit.

3. Add the egg yolks to the melted and cooled chocolate and mix until well combined. Add the cocoa powder and salt and mix in. Set aside.

4. Add the egg whites to a large bowl and mix on high speed until white and foamy. Gradually add the sugar and mix until the sugar has dissolved and stiff peaks form. Add about 1/4 of the whipped egg whites to the bowl with the chocolate and fold in. Gradually add more and gently fold in – you want to incorporate the whipped egg white so you do not see any streaks but you also want to keep as much volume as possible, so be very gentle ;) Pour the batter into the prepared springform tin and smooth out the top. Bake for about 30 minutes. Take out of the oven and let cool down in the baking tin for about 15 minutes, then loosen the sides and pull with the baking parchment onto a wire rack. Let cool down completely. Serve with some ice cream or whipped cream.