Barefoot Contessa (en-US)

1 pound French green lentils, such as le Puy
1⁄4 cup good olive oil, plus extra for serving
4 cups chopped yellow onions (2 to 3 onions)
4 cups chopped leeks, white and light green parts (2 leeks)
1 tablespoon minced garlic (2 large cloves)
1 tablespoon minced fresh thyme leaves
1 teaspoon ground cumin
Kosher salt and freshly ground black pepper
3 cups medium-diced celery (8 stalks)
3 cups medium-diced carrots (4 to 6 carrots)
3 quarts (12 cups) chicken stock, preferably homemade
1⁄4 cup tomato paste
1 pound kielbasa, cut in half lengthwise and sliced 1⁄3-inch thick
2 tablespoons red wine vinegar
Freshly grated Parmesan cheese, for serving

In a large bowl, cover the lentils with boiling water by 2 inches and allow to sit for 15 minutes. Drain and set aside.

Meanwhile, heat the olive oil in a large (12-inch) pot or Dutch oven, such as Le Creuset, over medium heat. Add the onions and leeks and saute for 15 minutes, stirring occasionally, until the vegetables are translucent. Add the garlic, thyme, cumin, 1 tablespoon salt, and 1½ teaspoons pepper and cook for 1 minute. Add the celery and carrots and cook for 10 minutes, stirring occasionally. Add the chicken stock, tomato paste, and reserved lentils and bring to a boil. Reduce the heat and simmer uncovered for 1 hour, adding the kielbasa after 30 minutes. Add the red wine vinegar, taste for seasonings, and serve hot in large bowls, drizzled with olive oil and sprinkled with grated Parmesan cheese.

Lentil Sausage Soup (updated)