Preheat the oven to 325 degrees F (165 degrees C). Cut a square piece of parchment paper that is larger than the springform pan. Set it on the bottom of the springform pan and secure the ring on top; the paper will extend outside of the springform pan, which makes it easier to remove the torte after baking. Grease the sides of the springform pan.

Melt butter in a saucepan over medium heat. Remove from heat and stir in chocolate until melted. Allow to cool lightly.

Beat egg yolks and 1/2 the sugar in a bowl with an electric mixer until light and foamy, about 5 minutes. It is important to beat a lot of air into the egg yolks, so they almost triple in volume.

Fold lightly cooled chocolate mixture into the egg yolk mixture using a spatula.

Beat egg whites in a glass, metal, or ceramic bowl until foamy using the electric mixer on medium speed. Gradually add remaining sugar and salt, continuing to beat until stiff peaks form.

Stir 1/3 of the egg whites into the chocolate batter to thin it out. Then carefully fold in the remaining egg whites using a spatula. Immediately transfer batter into the prepared springform pan.

Bake in the preheated oven until torte is no longer glossy, 30 to 40 minutes. Be careful not to bake too long, otherwise it will get dry.