Heat the oil in a heavy bottomed 6 quart stockpot over medium high heat.
Add the onion, carrots, leeks, celery, turnip, parsnip and mushrooms, and cook for 5 minutes.
Add the Sachet d'Epices and water.
Bring to a boil and quickly reduce heat to a simmer. Cook uncovered for 30 minutes, skimming the top as necessary.
Strain the stock through a colander to remove the large solids. Restrain through cheesecloth to remove the fine particulates.
Cool, and store the stock as described in the introduction.