Combine everything except the tomatoes, dairy, and spinach in the crockpot. Cook on low 8-10 hours.
30 minutes before serving, remove the bay leaves, add the tomatoes and pulse with an immersion blender to grind up about half the lentils. Stir in the half-and-half, and the spinach if using. Cook another 30 minutes. Serve hot with rice or couscous.