Rinse: Rinse the lentils thoroughly under cold running water and drain.

Optional Soak: If preferred, soak the lentils in cold water for a couple of hours before cooking, though most modern varieties do not require soaking.

Chop: Finely chop the onion, garlic, carrots, and celery.

Dice: Peel and dice the potato into small cubes.

Heat Oil: In a large pot, heat the olive oil over medium heat.

Cook Onion and Garlic: Add the onion and garlic and sauté until translucent, about 2-3 minutes.

Add Carrots and Celery: Stir in the carrots and celery, cooking for another 5 minutes while stirring occasionally.

Combine Lentils: Stir in the rinsed lentils, ensuring they mix well with the sautéed vegetables.

Add Tomatoes: Pour in the crushed tomatoes or tomato sauce, stirring to combine.

Add Broth and Herbs: Pour in the vegetable broth (or water). Add the bay leaf and rosemary sprig.

Cook: Bring the soup to a boil, then reduce the heat to low and let it simmer for 30-40 minutes, or until the lentils and potatoes are tender. Stir occasionally and add more broth if the soup becomes too thick.

Remove Herbs: Discard the bay leaf and rosemary sprig.

Season: Adjust the seasoning with salt and pepper to taste.

Plate: Serve the soup hot in bowls.

Garnish: Drizzle with extra virgin olive oil and sprinkle with fresh chopped parsley if desired.