There is an abundance of squashes and pumpkins on the market at the moment; the deep orange-fleshed varieties offer the best flavour and colour.
A good knob of butter
1 small leek, roughly chopped and washed
1 small onion, peeled and roughly chopped
1kg ripe, orange-fleshed squash or pumpkin, peeled, seeded and roughly chopped
1.5 litres vegetable stock
Salt and freshly ground black pepper
For the pesto
40g good-quality walnuts, lightly toasted
50g fresh basil leaves and any soft stalks
1 clove of garlic, peeled and crushed
A good pinch of sea salt
4tbsp freshly grated Parmesan
2tbsp freshly grated mature Pecorino (or use 6tbsp Parmesan)
100-120ml extra virgin olive oil (preferably a sweeter variety)
For the pesto: put the walnuts, basil, garlic and salt in a liquidiser and coarsely blend. Add the cheese and blend again briefly, then transfer to a bowl.
Gently cook the leek and onion in the butter in a thick-bottomed saucepan until soft. Add the squash and vegetable stock, bring to the boil, season with salt and pepper then simmer for 20 minutes.
Blend in a liquidiser until smooth, then strain through a fine-meshed sieve. Re-heat the soup and adjust the consistency with a little vegetable stock or water if necessary and re-season with salt and pepper. Serve with a spoonful of the pesto on top.