Heat the oil in a large pot over medium-low heat. Place onions in pot and cook 20 minutes, stirring occasionally until very tender and golden brown.
Step 2
Mix celery root, potato peels, carrots, mushrooms and squash into pot. Season with salt. Continue cooking 45 minutes or until vegetables are very tender and golden brown.
Step 3
Pour water into pot. Bring to a boil. Reduce heat to low and simmer 30 minutes, stirring occasionally. Strain out the solids, taste for sufficient salt and voila! Your stock!