I’m in a real soup phase at the moment, throwing whatever veg I have to hand in the fridge into my slow cooker and adding some flavours and pulses to thicken it up and give it some oomph – handy t keep it sitting on the side throughout the day to feed myself, Caroline, Small Boy when he comes home from school, Mrs J after work, and anyone else who strolls through the door. This was a Monday afternoon delight, a use-up for the stray carrots that were lolling around in the vegetable drawer to kickstart the week with a hefty dollop of vitamin C and some fire in our bellies.

CANNELINI BEANS: You can swap the beans for any beans, pulses or lentils that you prefer or have to hand; butter beans can go a little floury when cooked for any considerable length of time, but any others should be fine.

LEMONGRASS: If you don’t have lemongrass paste to hand – and I only do because it was substituted for garlic paste in my weekly online shop a while back – you can use 1 tbsp garlic and 1 tbsp lemon juice, and as ever, bottled lemon will be absolutely fine. The baking variety, rather than the cordial! For the truly accurate cook, I make 1tbsp lemongrass paste equal to 4.2 grams.

Makes 6 portions, from 23p each
300g frozen onion or two large fresh ones, 15p (50p/1 kg fresh onion)
800g carrots, 46p (57p/1 kg)
20g fresh ginger, 8p (38p/100g)
1 tbsp lemongrass paste, 6p (£1.25/95g)
1.2l chicken style or vegetable stock, 5p (50p/10 stock cubes)
400g canned cannelini beans, 55p
1 tsp paprika or a few pinches of chilli, 2p (£1.30/110g)
Plenty of black pepper, <1p (18p/100g)

If using fresh onions, first peel and dice them – neatness doesn’t particularly matter here, as they will all be whizzed up in the blender soon enough. Toss into a large, heavy bottomed pan.

Dice your carrots and add those too, and grate in the ginger. Add the oil, and bring to a medium heat for five minutes, stirring to disturb it all and prevent the onion and ginger from sticking and burning.

Pour over half of the stock, and spoon in the lemongrass, or lemon juice and garlic, and the paprika or chilli. Bring to the boil, then reduce to a simmer.

Drain and thoroughly rinse your beans, then simmer for 20 minutes until the carrot is soft and the beans nice and creamy.

Transfer the soup to a blender – you may need to do this in batches – and blend for 60 seconds at a time until smooth. Add additional stock to thin to taste, and serve.

I like to pour mine straight into the slow cooker at this stage and keep it warm all day – the additional cooking time sweetens the flavour and deepens it too, and means I have piping hot soup on demand, exactly when I want it!

All prices calculated at a major UK supermarket by best value available unit, and proportion used. This recipe was calculated at Tesco, and prices quoted are correct at the time of publication.