1. Heat oil in a large pot or Dutch oven over medium heat until shimmering. Add onion, carrot, rosemary, garlic, and 1/2 teaspoon salt and cook, stirring occasionally, until tender, about 5 minutes. Add lentils, bouquet garni, 1 1/2 teaspoons salt, and water. Bring to a boil, then reduce heat to a simmer, skimming off any foam that rises to the top.
2. Continue to simmer gently until lentils are completely tender, about 1 hour. Remove bouquet garni and discard. Working in batches, carefully transfer about three-quarters of soup to blender (about 5 cups) and puree until smooth; transfer remaining lentils to a medium bowl and set aside.
3. Melt 3 tablespoons butter in now-empty pot. Add spinach and parsley and cook, stirring frequently, until spinach has wilted, 1 to 3 minutes. Add pureed lentils, reserved lentils, and remaining 2 tablespoons butter and cook, stirring gently, until combined. Serve hot with sherry and pepper sprinkled on top.
Source: Hannaford fresh Magazine, March - April 2019