For the dough, line the troughs of a muffin tray (for 12 pieces) with paper cups. Finely chop the nuts. Mix flour, baking powder and baking soda. Whisk eggs in a bowl with sugar, vanilla sugar, oil and sour cream.
Stir in the flour mixture and orange peel briefly. Finally fold in the walnuts.
Spread the dough into the moulds and bake in a preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) for 20-25 minutes. Let them cool down.
For the icing sugar pour it into a bowl. Add egg white and mix with the whisk of the mixer to a thick icing. Use a knife to spread on the muffins and allow to dry.
Wash the carambola, dab dry and cut into slices. Sprinkle with lemon juice immediately. Dab carambolas and put 9-11 carambola slices on 1 wooden skewer, ending with 1 small slice as a star.
Halve the cherries and place them on the fruit slices as a Christmas ball. Decorate the muffins with the Christmas trees.