Preheat the oven to 160°C. Line a muffin tin with paper or parchment liners.
In a bowl, mix the whole wheat flour, sugar, baking powder, cinnamon, and salt. Add the muesli and mix well.
In another bowl, mash the bananas with honey to obtain a smooth puree.
Using an immersion blender, mix the eggs, oil, milk, banana-honey puree, and vanilla sugar.
Gently fold the dry ingredients into the wet ingredients, mixing until just combined. Carefully add the blueberries.
Fill the muffin cups about 3/4 full.
Decorate the surface of the muffins with a sprinkle of muesli and a pinch of cinnamon.
Bake for 25-30 minutes, until a skewer inserted in the center comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.