Preheat the oven to 200 ° degrees top / bottom heat. Set the circulating air to 180 degrees without preheating
Clean the rhubarb and cut into small cubes, also dice the marzipan.
Mix the brown sugar, oil, egg, vanilla sugar, yogurt and amaretto together in a bowl.
Then mix the flour, baking soda, baking powder and salt together in another bowl. Add to the liquid ingredients together with the rhubarb pieces and marzipan cubes.
Pour the batter into the (possibly greased and floured) muffin tin.
If the hollows are quite small, have some paper cases ready, because then the batter will be enough for about 15 muffins.
For the topping, stir the ingredients, spoon onto the unbaked muffins and place in the oven for about 30 minutes.