umpkin soup, so delicious in theory – sweet, velvety, lightly autumnal – is so often disappointing in reality. Thin in flavour and consistency, thanks to squash's high water content, it's likely to make even the most conscientious cook regret not chucking those Halloween offcuts on the compost heap when they had the chance. This, I hope it goes without saying, is not sort of pumpkin soup.

About 1½kg pumpkin or winter squash (eg, crown prince, sugar pumpkin, kabocha), washed

, or vegetable stock
1 large red or yellow onion, peeled and chopped
1 celery stick, cut into small dice
2 small carrots, peeled and cut into small dice
1 small red chilli, chopped, or a sprinkle of chilli flakes (optional)
(optional)
2 tbsp butter (optional)
4 sage leaves, roughly torn, or the leaves from 2 thyme sprigs (optional)
1 handful grated parmesan, or gruyere or similar (optional)
(optional)

1 A note on the pumpkin

The single most important step here is your choice of pumpkin. Look for something that feels heavy for its size. I like the dense, fudgy crown prince or a nutty kabocha, but, if all else fails, a butternut squash will do nicely. Asian, African and Caribbean grocers often stock a wider variety than supermarkets, as will your local greengrocer or farmers' market.

2 Skin the pumpkin

Pumpkins can be as much as 90% water, so it's worth roasting the flesh to concentrate its flavour. Heat the oven to 200C (180C fan)/390F/gas 6. Wash the pumpkin, then cut off some skin from one end so it will sit firmly on a board. Use a Y-shaped peeler or sharp knife to remove the rest of the skin and put the trimmings in a medium saucepan.

3 Deseed and chop the pumpkin

Cut the pumpkin into quarters, then remove the seeds (and the flesh around them). Add all but a spoonful of the seeds to the pan with the skin, and set aside the rest for now. Cut the flesh into large, evenly sized cubes and put these on a baking tray (use a second tray if there are too many to fit comfortably in one layer).

4 Roast the pumpkin

Drizzle the cubes with a little oil (olive is nice, but anything not too strongly flavoured will do) and toss with a little salt. Bake for about 40 minutes, until soft and beginning to brown. If the cubes are colouring unevenly, turn around the tray halfway and remove any that look as if they might burn before the rest are done.

5 Roast the pumpkin seeds

Wash the reserved spoonful of pumpkin seeds, if necessary, to remove any flesh clinging to them, then blot dry with a clean tea towel or kitchen paper. Put the seeds on a fresh tray and toss with a little oil and salt, then put them in the oven for the last 10 minutes of the pumpkin cooking time. Set aside to crisp up.

6 Boil the pumpkin offcuts

While the pumpkin is cooking, put the stock in the peelings pan – a good fresh chicken stock is my favourite, because it's richer and more neutral than vegetable stock, but most varieties will do, as will plain water. Bring to a boil, then turn down the heat and simmer gently for 30 minutes.

7 Start the soup base

Put two tablespoons of oil in a large saucepan on a medium-low heat, then add the onion, celery, carrots and a good pinch of salt, and fry, stirring regularly until soft but not brown. Stir in the chilli, if using, and fry for another minute or so (if the soup base is ready before the pumpkin is roasted, take the pan off the heat).

8 Add the roast pumpkin

Stir the roast pumpkin cubes into the soup base, then strain in the pumpkin-skin stock (discard the trimmings). Bring to a simmer and cook for about 10 minutes, or until the pumpkin is very soft. Puree with a stick blender or in a jug blender (if using the latter, let the soup mix cool slightly first), then taste and adjust the seasoning, adding a little sugar or diluting the soup with water, as necessary.

9 Finishing touches

If serving with browned butter (a drizzle of cold pumpkin oil is a good vegan alternative), heat the butter until golden, stir in the sage and decant immediately into a heatproof bowl or jug. Serve the soup topped with cheese, if using, a grating of nutmeg, a drizzle of the brown butter and sage or oil, and a few roasted seeds.