Soup is very quick to make and very forgiving. Cooking can be a precise art but not here – a few hundred grams or millilitres here and there won’t make much difference and it is so easy to adjust the thickness, creaminess, flavour etc. The only absolute cast iron requirement is some sort of onion; at a pinch you could probably get away with using a leek or two but there really is no substitute for a common brown or white onion unless making a bright and fresh summer soup in which case a spring onion or shallot will be an excellent choice.

Otherwise, play with what vegetables you use to your hearts content. There are, of course the tried and tested recipes that have stood the test of time. But you really can’t go wrong with any combination; just stick to common sense – fennel seed and coconut milk for example is never going to work but use a little Thai curry paste in the base of a butternut squash soup and the coconut milk suddenly makes perfect sense.

A tablespoon or two of double cream can add a wonderful silkiness to soup but here I am using a spiced butter and it is just so delicious swirled on top the fragrant combination of root vegetables, fennel and cumin seed. A touch of luxury to an otherwise everyday staple but worth its weight in gold in terms of nutrition, taste and culinary contentment. This soup freezes well.

Serves 8

2 tablespoons rapeseed or light olive oil
2 onions, chopped
1 large leek, chopped
2 cloves garlic, chopped
1 large stick celery, chopped
2 sweet potatoes, peeled and chopped
1 red pepper, deseeded and chopped
1/2 butternut squash, chopped (no need to peel)
2 medium beetroot, peeled and chopped
1 tablespoon fennel seeds
1 tablespoon cumin seeds, crushed
Pinch chilli flakes (optional)
2/3 good quality chicken or vegetable gel stock cubes
11/2 to 2 litres boiling water
Salt & black pepper

Heat the oil in a large pan. Add the onion, leek, garlic and celery. Cook until beginning to soften over a low heat. Add the fennel and cumin (chilli if using) and cook for a minute or two, then add the sweet potato, squash, beetroot and red pepper. Stir around for a bit and then add the stock to cover. You may not need it all. Season and then cover with a lid. Simmer for about thirty minutes until the vegetables are completely soft.

Blitz either in a liquidiser or use a hand held blender. Check seasoning and adjust thickness with any remaining stock. Serve with the spiced butter swirled over.

SPICED BUTTER

50g butter
1 teaspoon cumin seeds
1 teaspoon coriander seeds
1 teaspoon mustard seeds
Cinnamon stick
Black pepper

Crush the cumin and coriander seed in a pestle and mortar. Melt the butter and add with the cinnamon stick, pepper and mustard seeds. Heat until foaming and drizzle over the soup.
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