Preheat the oven to 200°C, fan 180°C, gas 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.
Cook’s tip: to freeze, cool the muffins completely, then freeze in a zip-lock bag for up to three months. Defrost at room temperature and reheat in a warm oven before serving.