How to Make It
In a large saucepan, cover the lentils with 3 inches of cold water, add the bay leaves and bring to a boil. Reduce the heat and simmer for 15 minutes. Add 1 tablespoon of the balsamic vinegar and a generous pinch of salt and cook until the lentils are tender, about 5 minutes longer. Drain; discard the bay leaves.
In a small bowl, whisk 1/3 cup of the olive oil with the Dijon mustard and the remaining 3 tablespoons of balsamic vinegar. Season with salt and pepper.
In a large skillet, heat the remaining 2 tablespoons of olive oil. Add the pancetta and cook over moderately high heat until lightly browned, 3 to 4 minutes. Add the leeks and cook until they begin to soften, 3 to 4 minutes. Add the lentils and cook, stirring, for 1 minute. Stir in the vinaigrette and chopped parsley, thyme and savory. Season with salt and pepper.
Transfer the lentils to a wide bowl and arrange the sausage slices on top. Garnish with the parsley sprigs and serve.