Brew a strong coffee and set aside 1/2 dl. to cool. Melt the butter in a small pot over low heat. In another bowl, whisk eggs, sugar, and vanilla seeds until it becomes a fluffy mixture. Whisk until it is light and very airy. Fold the flour into the fluffy egg mixture. Roughly chop the chocolate and melt it together with the butter in the pot. Remove the pot from the heat and let the chocolate melt slowly. Add the coffee and salt to the chocolate/butter mixture. Pour the now-tempered chocolate/butter mixture into the egg mixture. Stir well. Prepare a springform pan of approximately 22 cm by lining the bottom with baking paper: remove the ring, place a piece of baking paper over the bottom, and reattach the ring. Pour the batter into the pan and bake the cake at 175 degrees Celsius (347 degrees Fahrenheit) with fan for 20-25 minutes. The cake should be gooey in the middle when you take it out. Let it cool completely before adding the chocolate mousse on top. It’s even better if you make the cake the day before.  

Brew a strong coffee and set aside 1 dl to cool. Roughly chop the chocolate and melt it over a water bath on low heat. Set the melted chocolate aside and let it cool. Whip the cream to a light foam - be careful not to whip it stiff, as this will make the whipped cream grainy. Mix the cold coffee and melted chocolate together in a bowl. Stir 1/3 of the whipped cream into the chocolate mixture. Gently fold the chocolate mixture into the rest of the whipped cream. Be mindful of the temperatures to avoid the mousse separating. Let the mousse set a bit in the refrigerator before assembling the cake. It takes about an hour, but less time can also suffice.   You now have a cooled chocolate cake and a chocolate mousse ready for assembly. It’s best to assemble just before serving. Remove the chocolate cake from the springform pan, place it on a serving platter, and spread the chocolate mousse on top in your desired layer. Finally, decorate with fresh berries.