Hi Kathy,
Mushrooms were a treat when I was growing up.  My Mom and Dad loved them but they were not available commercially as they are today so we had to go out and pick them.  I was never happy about this springtime excursion as there was always the expectation that you actually had to find them.  (I was about 8.)  They were a type of field mushroom - called "pidpenky" or "hryby" in Ukrainian.  They were sort of like the small white button mushrooms we now buy.  On occasion if we happened to be in a woodsy area Mom would go looking for morels.  If she found a clump or two she'd become ecstatic!  The next job was even worse than the actually picking.  It was a very tedious job to clean those wild mushrooms.  Insects loved them as much as Mom and Dad did.  There was much trimming to be done!  Mom would preserve them in some fashion as they also played a part in our Lenten Christmas Eve meal. Dried mushrooms were treasured like gold.

We rarely had mushroom soup, but when we did it was a thinner version of the mushroom sauce that often graced a special meal.  The technique I use is straightforward.   One might say it is a cream sauce or brown sauce with mushrooms and thinned to the consistency of soup.

If I were to make it today I would likely:

Saute, in about 1/4 cup butter or fat of your choosing, in a large heavy based pan (a wok is great!) a finely chopped onion with a rib of finely chopped celery and then add at least 4 cloves of chopped garlic, (a small bay leaf adds flavour as does a pinch of thyme).  (Roasted garlic is terrific - I should tell you how I do mine.)  {If I had rendered chicken or pork fat I would use it.)  When all is very soft, add about a pound of cleaned sliced mushrooms and saute (medium heat) until the moisture has evaporated.  Add about 3-4 T of flour to make a roux - adding more butter (fat) if necessary.   I would add about 1/4 c of dry (white) vermouth to deglaze the pan and then add about 1-2 cups of really rich chicken broth.  Since I have not yet added salt, I would not hesitate to add several chicken bouillon cubes.  If I have no chicken stock on hand I would use more cubes and just use water.  (Save potato water and use it for extra flavour).  If I have dried mushrooms available (about 2 ounces) I would soak them for at least half an hour and strain the liquid through a coffee filter.  (They can leave quite a residue!)  Add the strained mushroom liquor to the pot and then the dried mushrooms - chopped up a bit.  Dried mushrooms add so much flavour!  Add freshly ground pepper and taste for salt.  The final flavouring agents are 2 T chopped fresh dill and some chopped parsley and about 1/2 cup of sour cream or whipping cream and just bring to a boil.  So that is the sauce!  If I were to make soup, I would use more chicken stock or thin with milk before the addition of the herbs and cream to achieve the desired consistency.
If cream or milk are not desired (as in my Lenten version - which, by the way, means vegan all the way) I might saute a small carrot, diced, with the onion and celery, just to add a bit more substance and flavour and I definitely use potato water for the liquid.  When making this version I cook potatoes (for another purpose) in lots of water and save the potato broth.
This is not likely how you hoped to get a recipe. I do go on...and on...and....

It is obvious that some things can be omitted and others added.  I do a lot of tasting before I serve anything so I might need to perk the soup up with a hint of cayenne or add more herbs.  If I think I want it thicker because this may be the "main course" I may add a handful of frozen peas and maybe some leftover chicken bits before the final addition of cream. 

Of course a can of sliced mushrooms instead of fresh is always a possibility.  I used to use them before fresh mushrooms were affordable.  I did use the liquid from the can but I prefer my potato water.

By the way,  I too graduated with a BSc in Household Economics with a food major (many many years ago - I am almost 73!).   It was my mother's dream to be a home ec. teacher (she taught grade 2) and so hoped I would follow that path.  I ended up doing an internship in dietetics and became a dietitian.  I worked in that field for a couple of years until I began my family.  I now live alone but I still cook daily for myself and the odd friend or two.

I do enjoy your Blog.  Of course I am not in need of basic instruction but I can still learn many things.  A friend recently said she wanted a recipe for "fried rice".  Off the top of my head I said how I might go about it.  Then I thought, why don't I find a recipe that this relatively inexperienced cook might use.  That is how I found your Blog and was delighted to find our techniques and ingredients were the same!  So, I will be checking in frequently just to make sure I am doing things right.
Keep up the excellent work.  You ARE the Home Ec. teacher you were in a classroom!

Cheers! 
Chris Ulan