- Put the potatoes, mushrooms, garlic, bay leaf, savory, marjoram, and salt and pepper into a medium-size stockpot.
- Cover with about 6 cups of cold water.
- Cook over medium heat until it boils, then reduce heat and cook for 20 to 30 minutes.
- In a separate small saucepan, heat the cooking oil over medium-high heat.
- When hot, sprinkle in the flour and shallots.
- Brown in order to make a roux, stirring constantly.
- Add some of the cooking liquid from the soup to thin the roux out and then pour it into the soup.
- Bring to a gentle boil and remove from heat.
- Add the tarragon vinegar before serving.
- Then garnish with chopped chives and sour cream.
- For a lighter version add low-fat sour cream.