Apple-cinnamon muffin with walnut crumb

I'm already in Christmas mood, especially when the cinnamon apple started to flavour from the oven. These muffins are simple (the recipe can be sum up in 3 steps) but delicious, soft and very Christmasish :)

Ingredients (6 pieces):
1 egg
1,5 dl yoghurt
3,5 dkg butter or marge
12 dkg flour
1 teaspoon cinnamon
pinch of salt
8 dkg sugar
10 g vanilla sugar
1 teaspoon baking soda
1 middle-sized apple

For decoration:
1 handful walnut + 1 tablespoon sugar

1. In a big bowl mix the egg and yoghurt. In another one mix the flour with the baking soda, salt, cinnamon, sugar then add the egg mixture and grated apple to this.Mix all the ingredients properly.

2. Preheat the oven to 200°C. 

3. Spoon the dough into the muffin paper lined forms, sprinkle with sugar-walnut mix and bake in the preheated oven for about 20-30 minutes.