Heat the olive oil in a large pot or dutch oven over medium high heat. Season the chicken with salt, pepper, and the celery seed on both sides. Add to the pot, skin side down, and scatter the thyme sprigs around the pot. Cook the chicken about 5 minutes per side, then add the marsala wine, allowing most of it to evaporate while the chicken finishes cooking.

Take the chicken out of the pot and tent with foil. Remove the thyme stems. Add the butter, shallots, leeks, and a pinch of salt, stir to combine. Cook for a few minutes until the leeks are softened. Add the carrots, potatoes, and another pinch of salt, cook 5 more minutes.

Add the chicken stock, lentils, and bay leaf. Bring to a boil over high heat. Lower the heat to medium and simmer, partially covered, for 15-20 minutes. Meanwhile remove the skin form the chicken and shred into bite size pieces.

When the lentils have fallen apart and thickened the stew, remove the bay leaf and add the shredded chicken and spinach; stir. Cook for a couple more minutes to warm the chicken and wilt the spinach. Off the heat, add the vinegar and season with salt and pepper to taste.

Ladle into bowls and top with parmesan cheese.