1. Prepare Your Ingredients: Chop the onion, mince the garlic, dice the carrots and celery or celeriac, rinse the leeks thoroughly, and rinse the French lentils under cold water.

2. Cook the Bacon: In a large stock pot or Dutch oven, cook diced bacon over medium heat until golden brown and crisp. Once done, remove the bacon and set aside, leaving the rendered fat in the pot.

3. Sauté the Vegetables: Add the onion, garlic, carrots, celery or celeriac, and leeks to the pot with the bacon fat. Sauté until the vegetables are softened and beginning to caramelize, releasing their natural sweetness and aroma.

4. Add Lentils and Broth: Stir in the rinsed French green lentils, then pour in the chicken or vegetable broth. Add thyme, bay leaves, and a tablespoon of red wine vinegar to elevate the soup’s flavor profile.

5. Simmer the Soup: Bring the mixture to a gentle boil, then reduce the heat to low and partially cover the pot. Let the soup simmer for 30-50 minutes, or until the lentils are tender but still hold their shape. Stir occasionally to ensure even cooking.

6. Season the Soup: Taste the soup and adjust the seasoning with salt and pepper as needed. If desired, add optional ingredients like Herbes de Provence, canned diced tomatoes, or a bouquet garni for added richness.

7. Blend (Optional): For a creamier texture, use an immersion blender to purée part of the soup (around 20%) or mash some lentils against the side of the pot using a spoon. This will thicken the soup while maintaining a hearty texture.

8. Serve and Garnish: Ladle the soup into bowls and garnish with the crispy cooked bacon and fresh parsley for added flavor and presentation. Optionally, stir in a dollop of Greek yogurt or sour cream for a tangy twist.

9. Store Leftovers: If you have leftovers, let the soup cool completely before transferring it to an airtight container. Refrigerate for up to five days or freeze for up to three months. Ensure proper reheating for future servings.

10. Reheat: Rewarm the soup gently on the stovetop over medium heat, adding extra broth or water if it has thickened too much. Stir occasionally for even heating. Alternatively, reheat in the microwave in short intervals, stirring in between.