Heat the oven to 200C/fan 180C/gas 6. Line a 12-hole muffin tin with muffin cases. Tip the flour, baking powder, almonds and sugar into a large bowl. Mix the mashed banana with the nut butter, eggs and yogurt until the mixture is smooth, using a hand blender if you have one. Fold the wet mixture and the dry mixture together along with the chopped banana and half the flaked almonds – don’t worry if it looks a bit lumpy.
Divide the mixture between the cases and bake for 15-20 minutes, or until the muffins have risen and are golden. Cool.
Mix the icing sugar with a little water to make it runny enough to drizzle, but thick enough not to run off the muffins. Spoon a little onto each muffin and add some flaked almonds.