2 cups chopped leeks
1 cup chopped carrots
1 cup chopped celery root
1 1/2 cups chopped celery
1 1/2 cups chopped mushrooms
2 cups chopped kale
4 cloves garlic, sliced
1 cup red lentils
1/2 teaspoon freshly ground black pepper, or to taste
1/2 teaspoon crushed red pepper flakes
1/2 cup no-salt-added tomato paste (see note)
4 cups no-salt-added or low sodium vegetable broth
3 cups water
6 cups spinach or baby kale