This red lentil soup is one of my all-time favorite dinners. Sautéed leeks and onions are combined with carrots, celery, crushed tomatoes, chicken broth, and red split lentils (which cook quickly!) to produce a hearty, thick lentil soup that is naturally gluten-free, nutritious, and filling. This soup tastes even better as leftovers and can be frozen and prepped ahead.
In a large soup pot, melt the butter and extra virgin olive oil over medium heat until lightly bubbling. Add the onions, leeks, and generous sprinkling of kosher salt, and sauté, stirring occasionally, until the onions and leeks are soft and translucent in color, about 10 to 15 minutes. I place the pot lid on askew, to help trap moisture and ensure the ingredients sweat, soften properly, and don't gain too much color.
Add the carrots, celery, and garlic, stirring occasionally, for about 3 to 4 minutes. Continue seasoning the soup lightly with salt and pepper as you add the remaining ingredients. Add the lentils, crushed tomatoes, parmigiano-reggiano rinds, bay leaves, and chicken broth. Stir together and bring to a boil. Reduce the heat to medium-low and slowly simmer, uncovered, for about 30 to 40 minutes, stirring every 10 minutes or so, or until the vegetables are tender and the lentils have cooked through and broken down quite a bit. The soup should be thick and hearty.
Blend a small portion of the soup with an immersion blender (or transfer a large ladleful of soup to a small food processor or blender, and puree until roughly smooth). This step is optional, but creates a wonderful texture.
Season the soup with salt and pepper to taste. If it tastes at all flat, feel free to add a small squeeze of lemon juice (however, I like it just as it is!). Before serving, remove and discard the bay leaves and parmigiana cheese rinds. Serve hot. Garnish with freshly grated parmigiano cheese, if desired.
Tips for Success:
Older lentils tend to dry out and might take significantly longer to cook.Try to find a bag at the grocery store or choose them from a bulk bin that gets refreshed often (i.e. not the bag of lentils that has been sitting in your convenience store for three years on the top shelf).
Make Dairy Free: Substitute the butter for extra virgin olive oil, and omit the parmigiano rinds.
Make Vegetarian: Use vegetable broth in place of chicken broth.