My (german) MIL makes it around this time every year, and it is somehow both festive, yet not too much, and gorgeous with a cup of tea/coffee/glass of wine
It also has the advantage of being absolutely fail-safe and really, really easy!
250 g butter 250 g sugar 250 g flour, mixed with 1 sachet baking powder (or use sr flour (which is not available in germany, but I'm sure would work) 4 eggs 125 ml red wine (my MIL infuses it with mulled wine spices to make it more Christmassy) 1 sachet vanilla sugar (or 1 tsp vanilla essence) 1 tsp cinnamon 2 tbsp cocoa (the good stuff - unsweetened cocoa powder)
Mix everything together in mixer (I did it butter + sugar first, then eggs, then the rest, but my MIL says she just bungs everything into the mixer and blitzes it). Mix until it is a smooth and creamy batter. Pour into greased cake tin (she does it in either a loaf tin or the round one with a hole in the middle), and bake at 160°C for 1 hour. Skewer stuck in should come out clean when it's done.
That's it! I know it sounds very plain, but it's really light, satisfyingly chocolatey, yet moist because of the red wine, and keeps well. We've had it with strawberry icecream as a dessert, but would also be good with cream (or indeed is lovely on its own too).
(Also - you can do it with red grape juice if you want to do a non-alcoholic version, it's still nice)