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One of the cheapest dinners you can put on a table, and one of the few that genuinely takes half an hour from a cold start.
Red lentils are not like other lentils
They need no soaking and they collapse completely as they cook, which is the point — they thicken the soup themselves and you end up with something creamy without any cream.
Do not substitute green or brown lentils here. Those hold their shape, take far longer, and give you a completely different (perfectly nice, but not this) soup.
Rinse the lentils in a sieve until the water runs clear. It takes twenty seconds and removes the dust that otherwise makes the soup taste faintly muddy.
Bloom the spices — this is the step that matters
Adding ground spices to liquid gives you a dusty, slightly raw taste. Frying them in oil for about a minute first, once the onions are soft, changes them completely: the flavour compounds are fat-soluble and they need the oil to release.
Thirty to sixty seconds, stirring constantly, until they smell fragrant. Any longer and they burn and go bitter.
The lemon at the end is not optional
Lentils are earthy and the soup tastes flat and heavy without acid. A good squeeze of lemon stirred in at the end lifts the whole pot, and it is the difference between a soup people finish and one they do not.
Add it off the heat, taste, and add more if it still tastes dull rather than reaching for more salt.
For younger or more cautious eaters
It blends to a completely smooth purée, which suits anyone who objects to texture — the same approach as our hidden-veg tomato soup. Leave the cumin and coriander out, or halve them, for a milder version.
Storage
Thickens considerably in the fridge; loosen with a splash of water or stock when reheating. Keeps three to four days refrigerated, freezes two to three months, per standard soup guidance.
