Preheat the oven to 200°C/fan 180°C/gas mark 6. Line a 12-hole muffin tin with paper cases.
Sift the flour and baking powder into a large bowl. Stir in the carrot, courgette, spring onions and ground nutmeg and stir until combined.
In a jug, whisk together the soured cream, milk, egg and melted butter and pour into the dry mixture. Stir quickly to combine, but be careful not to over mix.
Divide between the muffin cases and bake in the centre of the oven for 25 minutes. Allow to cool slightly in the tin, and serve warm.