Put peppercorns and fresh herbs in cheesecloth and tie corners together to form a little package.
In large pot, bring broth, lemon juice, and cheesecloth package to a boil.
Add lentils and potato. Reduce heat, cover and cook for about 20 minutes.
In the meantime, in a nonstick skillet, carmelize onion and garlic with the butter. Once carmelized, add 2 cups of water, the carrots and cilantro and cook until carrots are softened.
Once potatoes are cooked properly, add onion mixture and cook for about 5 minutes more. Add salt and pepper to taste. If soup is a little too chunky, adding a cup or two of water helps thin it out a little bit. Remove cheesecloth package before serving.