Why a flexible soup beats a fixed recipe

By the middle of October the allotment stops being a set of tidy rows and becomes a puzzle. There is a bucket of carrots, a drawer of beetroot, four leeks that never quite fattened up, and a kale plant that has quietly turned into a small tree. A rigid recipe is no use here. What you want is a method that absorbs whatever you have and turns it into something you actually look forward to eating after a cold, muddy afternoon.

Think of it as a rough ratio rather than a list of ingredients: about a kilogram of roastable roots, a couple of onions or leeks, a generous handful of greens, a litre and a bit of stock, and herbs at both ends of the cooking. Everything else is negotiation, and the negotiation usually ends well.

Roast first: the single step that adds depth

Boiled roots make a thin, sweet soup that tastes of very little. The same vegetables roasted until their edges catch will give you a soup with real savour in it, and it costs you nothing but an oven shelf. Cut carrots, parsnips, swede, celeriac and turnip into rough 3cm chunks — no need to be neat — and tumble them into a roasting tin with a sliced onion, a halved head of garlic, a few sprigs of thyme and a good glug of rapeseed oil. Salt them now, not later.

Roast at 200°C (180°C fan, gas 6) for 35 to 45 minutes, turning everything with a spatula twice so the pieces caramelise on more than one side. You are looking for deep brown patches and a tin that smells sweet rather than burnt.

Beetroot is worth roasting in its own tin if you would rather your soup wasn't uniformly magenta — though a pink soup with a swirl of cream is no bad thing in November. Squash, pumpkin and Jerusalem artichokes behave beautifully here too. Potatoes are the one exception: they go gluey if roasted in quantity, so boil them separately or leave them out altogether.

What to add from the plot, and when

Timing matters more than the ingredients list. Some things want the whole cooking time, some want five minutes at the end.

• Roots and alliums — carrots, parsnips, swede, celeriac, beetroot, onions, shallots, garlic: roast them together from the start.
• Greens — kale, cavolo nero, chard, spinach, savoy cabbage: shred finely and stir in for the final five minutes so they keep a bit of bite and colour.
• Beans and peas — runner beans, French beans, borlotti, fresh peas: cook separately in salted water and add at the end. Frozen or overcooked, they turn grey and sad.
• Herbs — thyme, rosemary, bay and parsley stalks go in early; parsley leaf, chives, lovage and dill go in once the heat is off.
• The last green tomatoes — halve them and roast alongside the roots. Their acidity stops the finished soup from being cloying.

The method, in order

Once you have the principle, the whole thing takes about twenty minutes of actual attention.

• Heat the oven to 200°C (180°C fan, gas 6) and get the roots roasting.
• While they cook, soften your onions or leeks in a large heavy pan with butter or oil over a low heat for ten minutes. You want them translucent, not coloured.
• Tip in the roasted vegetables, scraping the tin with a splash of water so nothing good is left behind.
• Cover with stock — roughly 1.2 litres per kilogram of vegetables. Use a light chicken or vegetable stock, and be cautious with cubes: one per litre and a half is plenty, because you can always add salt later and you cannot take it out.
• Add a bay leaf, a few peppercorns and the parsley stalks. Simmer gently for 15 to 20 minutes.
• Stir the shredded greens through for the last five minutes.

Blend lightly, season properly

A stick blender is the right tool, used in short pulses. Stop while there is still some texture — a soup with a little body to it eats like a meal rather than a purée. If you prefer it silky, blend half the pan and stir the rest back in. Loosen with milk, a splash of cream or the water you cooked the beans in if it is too thick.

Then taste, and taste again. Soup needs more salt than you think, added in stages. A squeeze of lemon juice or a few drops of cider vinegar at the end will lift the whole pot. If it tastes flat and sweet — common with parsnip and beetroot — that acidity is usually what is missing. A pinch of sugar does the opposite job for a bitter kale-heavy batch.

Freezing portions for busy evenings

Let the soup cool within an hour, then portion it while it is still slightly warm; it pours far more easily. Flat freezer bags are the most space-efficient option, laid on a tray until solid, but 500ml tubs are simpler if you have the shelf room. Leave a couple of centimetres of headroom whatever you use.

It keeps well for three months. Reheat gently rather than boiling hard, adding a splash of water to loosen, and finish with fresh herbs — the ones frozen in the pot will have faded. Add cream or yoghurt after reheating, never before freezing, as dairy splits. Do the same with potatoes: a potato-heavy soup reheats grainy, so eat those batches fresh. Everything else tastes better on a dark Tuesday in November than it did on the day you made it.