Preheat the oven to 210 ° C (convection). Melt the chocolate and butter together in a water bath (do not overheat!). Beat the eggs with salt and flour until frothy, stir in the cocoa and sugar. Stir in the melted butter and chocolate mixture.
Fill the chocolate mass into 12-14 paper cases, taking care not to fill the molds too full! Bake in the preheated oven for about 6 minutes at 210 ° C.
The baking time depends heavily on the type of oven and may have to be tested yourself (e.g. take a muffin out for a test after 5 minutes and cut it - the classic toothpick test does not help with these chocolate muffins).