Preheat the oven to 250F. Position the oven rack in the middle of the oven.

Butter a 9-inch springform pan all along the bottom and sides of the pan. Cut out a parchment circle the size of the bottom of the pan and line the springform pan with the parchment paper.

Place the springform pan in the middle of a half-sheet baking sheet. Set aside.

Boil a liter of water.

Crack open all the eggs and remove all the chalazas.

Cut the butter into cubes and place it in a 4-quart saucepan.

Chop the chocolate and put it in the saucepan with the butter.

Heat the butter and chocolate over very low heat, stirring constantly.

Once the butter begins to melt, stir the mixture until the chocolate is completely melted and mixed with the butter.

Using a stand mixer, mix your eggs on low to break them up. Increase the speed to medium low.

Slowly stream the sugar into the eggs as they whip. Once all the sugar is added, whip the eggs on medium high until they quadruple in volume.

During the last 2 minutes of whipping, check your butter and chocolate mixture. Rewarm it if necessary.

Once the eggs are ready, reduce the speed of the mixer to medium-low. Stream in the chocolate mixture very slowly.

Add the salt and whip until all the chocolate is incorporated.

Remove the bowl from the mixer and give the mixture 2 or 3 stirs with a silicon spatula.

Pour the cake batter into the springform pan.

Place the baking sheet with the springform pan onto the middle rack of the oven. Carefully pour boiling water into the baking sheet.

Bake the cake for 2 hours. Check if the cake is baked or still jiggly.

Allow the cake to cool for about 30 minutes. Carefully lift the springform pan off the baking sheet.

Allow the cake to cool completely.

Run a pairing knife around the edge of the cake and release it from the springform ring.

Wrap the cake and chill it in the fridge for at least 6 hours, preferably overnight.

Slice the cake using a hot chef’s knife.

Garnish each slice with whipped cream, toasted hazelnuts, strawberries, or fresh raspberries if desired.