Why a flask of soup suits a riverside walk

A winter riverside walk is rarely a route march. It is two or three slow miles of stopping: watching a grey wagtail bobbing on a gravel bank, following a ripple that might be a trout, noticing where the current has undercut the roots of an alder. That sort of walking takes longer and burns less than you expect, and it chills you in a way a brisk uphill mile never does. Standing still is the coldest thing you can do outdoors. So the walk needs a warm, unhurried reward at its midpoint, and a flask of thick soup is exactly that.

The trick is not the recipe. It is the preparation — a hot flask, a soup with some body to it, and a place to sit out of the wind.

Preheat the flask or the soup will be tepid by the bridge

This is the step most people skip, and it is the one that makes the difference. A vacuum flask is cold metal or cold plastic inside when it comes out of the cupboard, and your soup spends its first hour warming the flask rather than itself.

• Fill the flask with boiling water, screw the lid on, and leave it for five minutes.
• Tip the water out — into the sink, or over a doorstep if it is icy — and fill immediately with hot soup.
• Fill to within a centimetre of the neck. Air space is heat loss.
• Screw the lid down firmly, then wrap the flask in a tea towel or a spare woolly hat.
• Carry it upright in the rucksack, not lying down, and pack something soft around it.

Done properly, a decent flask will still be genuinely hot four hours later. Done carelessly, it will be lukewarm by the time you reach the second stile.

A soup thick enough to stand a spoon in

Thin soup leaks, sloshes and cools fast. You want something dense and slightly rustic, the sort of thing that coats the back of a spoon. A lentil and root vegetable soup is ideal and costs very little.

Soften a chopped onion, two carrots, a stick of celery and a handful of diced swede in a little oil. Add a teaspoon of cumin or fennel seed, 200g of red lentils, a tin of chopped tomatoes and a litre of vegetable stock. Simmer for 25 to 30 minutes until the lentils have collapsed, then blend about half of it and stir it back in, so the soup keeps some texture. Season well — cold air dulls flavour, so be braver with salt and pepper than you would be at the kitchen table. A knob of butter or a drizzle of olive oil at the end makes it feel like a proper lunch rather than rations.

If it looks too thick to pour into the flask, loosen it with a splash of stock, not water. It should still ribbon off the spoon.

Bread, spoon and the small bits of kit

• A small crusty roll or a cheese scone. Butter wrapped separately in greaseproof paper, or left out entirely if the walk is short.
• A long-handled spoon — a dessert spoon, not a teaspoon. A spork works at a push.
• A napkin or a clean cloth, which doubles as a lid-holder when the flask is hot.
• A sit mat or a folded square of closed-cell foam. Cold benches steal heat through your legs.
• Gloves you can write in, or a pair of fingerless ones kept in the outer pocket.

All of it fits in the top of a day sack beside a small notebook and a pencil.

Finding a bench worth sitting on

Look for a bench that faces downstream, or at least across the water rather than into the prevailing wind. A hedge behind you is worth more than a view in front of you. Church porches, bridge parapets, a fallen trunk above the flood line and the leeward side of a stone wall all do the job when there is no bench at all.

Sit still for ten minutes and the river will start to show you things. Dippers work upstream in short flights, disappearing and reappearing. Grey wagtails pump their tails on the shingle. A heron will stand through your entire lunch if you keep your movements small. In the quiet of a cold afternoon you may hear a kingfisher before you see it — a thin, sharp whistle, low over the water. Redwing and fieldfare strip berries from hawthorn along the bank, and the first lesser celandine or snowdrop in a sheltered corner is worth noting.

Pour the soup into the flask lid or a small enamel mug, and eat slowly. There is no reason to hurry this part.

Journal while the soup cools

A nature journal earns its keep when you write in it before you have warmed up again. Keep it plain and factual — five or six lines is plenty.

• The date, the time you sat down, and the nearest village or a grid reference.
• Weather: cloud cover, wind direction, whether the air feels damp or dry.
• Water conditions: high or low, clear or peaty brown, fast or sluggish.
• What you saw and heard, with question marks where you are unsure. A possible otter spraint is a perfectly good entry.
• One small sketch of the thing that interested you most — a riffle, a root plate, a footprint in mud.
• Anything in flower, and the soup itself, since you will want to know next year what worked.

Uncertain identifications can be checked at home in the warm. The point of the journal is not to be a field guide. It is a record of attention: proof that you sat by a stream in January, ate something hot, and noticed what was there.