Lentil Soup

Method

1. sweat9 min
   medium, lid ajar, no browning
   olive oil + onion + carrot + celery + a pinch of the salt, until the onion is translucent and slumped — pull the sweetness out with steam rather than color, because a browned mirepoix reads as roast and fights the earthiness of the lentil
2. toast1 min
   medium, stirring constantly
   + garlic + cumin + coriander, until fragrant; ground spices are fat-soluble and only release into oil, so thirty seconds here does more than a teaspoon more added to the pot later — and thirty seconds is also the margin before the garlic scorches bitter
3. caramelize2 min
   medium, spread thin
   + tomato paste, smeared across the pan bottom until it darkens from red to brick and stops smelling raw; this cooks off the tinny note and builds the savory floor the soup otherwise lacks with no meat in it
4. simmer35 min
   bare simmer, partly covered
   + lentils + tomato + stock + water + bay leaf + black pepper, until the lentils are tender to the tooth but still holding shape. Keep it below a rolling boil: a hard boil batters the skins off, and the loose skins float while the interiors turn to paste. Add the lemon only later — acid early sets the pectin in the seed coat and the lentils will sit gritty for an hour without softening
5. mash2 min
   off heat
   crush about a quarter of the soup against the side of the pot with a spoon or a few pulses of a stick blender, then stir it back in — the released lentil starch thickens the broth so it clings, which is what separates soup from lentils sitting in stock
6. season2 min
   off heat
   + remaining salt + lemon juice + optional spinach, which wilts in the residual heat in under a minute. Taste before and after the lemon: the acid is what makes the cumin legible, and a lentil soup that tastes flat is almost always short on acid rather than salt