When hot, add oil, then add onion, carrots, leeks and celery, reduce heat and cook about 4 to 5 minutes, stirring.
Add the tomato paste and cook 2 minutes, stirring.
Add the broth, bay leaf and lentils and bring to a boil.
Reduce the heat, cover and simmer until halfway cooked, 20 minutes.
Add the butternut and cook until tender, about 15 minutes more. Discard the bay leaf, season with salt and pepper, to taste.
Add the kale and cook 7 minutes longer until the kale is tender.
Notes
To Freeze: Let the soup cool then transfer to a freezer-safe container. Keep frozen for up to 3 months.
To reheat, transfer to the refrigerator the night before then reheat on the stove or microwave.