Melt the butter in a saucepan together with the beer
Add muscovado sugar, sugar, and cocoa powder to the saucepan and let it simmer for a couple of minutes
Put the crème fraiche, vanilla sugar, and eggs in a bowl and whisk together until it becomes frothy and airy.
Pour the contents of the saucepan into the bowl and gently fold together with a spatula.
Sift flour, baking powder, and baking soda into the mixture.
Grease your springform pan with butter, oil, or use baking paper to line it.
Pour the mixture into the springform and don't be nervous, even though it is quite thin.
Bake the cake at 175 degrees Celsius (347 degrees Fahrenheit) (conventional oven) for 50-55 minutes. Check the cake after 45 minutes with a skewer or similar. Insert it into the center of the cake; if it comes out with batter, it's not done.
Remove the cake from the oven and let it cool on a rack.