I have a recipe from WDW for potato soup that describes the basic method. You could substitute veggies as desired. I never use an actual "recipe" for mine. I learned how to make it from my grandmother. She made the
best potato soup ever!

However, she never used any broth...just milk. She'd just cook onions in butter until they were translucent, pour milk into the pot, add the potatoes, cook until until they were soft & then thicken with a roux she'd make on the side.
When I was first married DH & I often had cream of mushroom soup that I'd make from scratch. I'd just "wing" it (no recipe) but saw this one that sounds like what I did. For some reason it's a different order than the potato soup.
Mushroom Soup
3 T. butter or margarine
1/2 c. sliced mushrooms
3 T. all-purpose flour
1 c. milk
Salt and freshly ground pepper to taste
Melt the butter in a small saucepan over moderate heat. Add the mushrooms and sauté for 2 to 3 minutes, stirring frequently. Add the flour and stir until the mixture had formed a paste and the flour and the butter are thoroughly incorporated. Add the milk and stir with a whisk or spoon until the paste is completely dissolved. Bring the sauce to a boil, stirring frequently. Season with salt and pepper. Makes about 1 1/2 cups.
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LOADED POTATO SOUP
from Olivia's, Old Key West Resort
1½ lb potatoes, baked, coarsely diced
3 oz broccoli, diced
3 oz onion, diced
¼ tsp white pepper
4½ oz sour cream
1 1/3 qt chicken broth
3¾ oz roux*
GARNISH
cheddar cheese, shredded
bacon bits
Bring chicken broth to boil. Add onions, broccoli and pepper. Boil 10-15 minutes or until broccoli is tender. Add potatoes. Bring to boil. Add roux, stirring constantly. Reduce to simmer 10-15 minutes. Fold in sour cream. Simmer 5-10 minutes. Garnish with shredded cheese, top with bacon. Serves 10.
*Roux
1 2/3 lb butter
1¾ lb all-purpose flour
In saucepot, melt butter. Slowly add flour, stirring constantly to avoid lumps. Cook 10-20 minutes (med low heat). Roux should be smooth with almond aroma. Quickly remove from heat.