Start the stew: Set a large heavy pot or Dutch oven over medium heat.

Start the stew: Add the olive oil to the pot and let it warm for about 30 seconds.

Cook the vegetables: Put the leeks, fennel, carrots, celery, and 1 teaspoon of the salt into the pot.

Cook the vegetables: Cook the vegetables for 8 minutes, stirring every minute or two, until the leeks are soft and the fennel and carrots have started to lose their raw crunch.

Build the base: Add the garlic and ground cumin to the pot.

Build the base: Cook for 1 minute, stirring often, until the garlic smells fragrant and the cumin is evenly mixed through the vegetables.

Simmer the lentils: Add the rinsed lentils to the pot and stir for about 30 seconds so they are coated with the oil and vegetables.

Simmer the lentils: Pour the vegetable broth into the pot and raise the heat to medium-high.

Simmer the lentils: Bring the broth to a boil, then lower the heat so the liquid stays at a gentle simmer.

Simmer the lentils: Partly cover the pot and cook for 20 minutes.

Simmer the lentils: Stir the stew and check a few lentils. If they are still firm in the center, keep simmering for 8 to 12 minutes more, until the lentils are tender but still hold their shape.

Make the topping: While the lentils finish cooking, put the yogurt, dill, and the remaining 1/2 teaspoon salt into a small bowl.