Cook bacon in a large soup pot over medium-low heat until most of the fat has rendered and your bacon is crisp. Let the bacon cool on a paper towel-lined plate and roughly chop half for garnish and chop the other half finely for the meatballs.
4 strips bacon
Cook the onion, carrot, and celery in the bacon fat over medium heat until softened and just starting to brown, about five to seven minutes.
1 yellow onion, 1 carrot, 1 celery stalk
Stir in the garlic and tomato paste and cook for about a minute until the garlic is fragrant and the tomato paste darkens slightly. Add the white wine, bring it to a boil, and scrape up any brown bits that have stuck to the bottom of the pan.
4 cloves garlic, 1 tablespoon tomato paste, ¼ cup white wine
Add the black lentils, broth, a tablespoon of Dijon mustard, salt, pepper, and bay leaf. Cover and cook at a simmer, stirring occasionally until the lentils are tender, about 25 to 30 minutes. Add a half cup of water or broth if the lentils are absorbing all of the broth and the soup looks dry.
1 teaspoon salt, 1 teaspoon ground black pepper, 1 bay leaf, 2 cups black lentils, 1 quart chicken or vegetable broth, 1 tablespoon Dijon mustard