Kraft has a lentil soup recipe that only takes four ingredients. Epicurious magazine has a French lentil soup recipe that is more complex but is still relatively easy.
To make Kraft's lentil soup, combine two large peeled, chopped carrots, one large chopped onion, 1 1/2 cup of uncooked red lentils and 6 cups low-sodium chicken broth in a saucepan, and bring the mixture to a boil. Simmer on medium-low heat for 30 to 45 minutes or until the vegetables are fork-tender. Run the soup through a blender in small batches until it is smooth.
To make the Epicurious recipe, heat 3 tablespoons of extra-virgin olive oil over medium-high heat in a large saucepan. Add 2 cups chopped onions, 1 cup chopped celery, 1 cup chopped carrots and two chopped garlic cloves. Saute the mixture for 15 minutes or until the vegetables begin to brown. Add 4 cups vegetable broth, 1 1/4 cups of drained, rinsed lentils and one 14.5-ounce can of diced tomatoes in juice. After bringing the mixture to a boil, reduce heat to medium low, cover and allow the mixture to simmer for 35 minutes or until the lentils are tender.
Puree 2 cups of the soup until it is smooth, and return the puree to the pan. If the soup is too thick, thin it by adding vegetable broth 1/4 of a cup at a time. Salt and pepper the soup, add a splash of vinegar if desired, garnish with celery leaves, and serve.