Homemade Cream of Mushroom Soup

We have been determined to stop eating canned soup and pre-made seasoning packets because they are LOADED with sodium and thousands of ingredients that you can't pronounce. I made this a few days ago for a casserole and it was actually really good!

Homemade Cream of Mushroom Soup
1/2 cup sliced mushrooms
3 Tablespoons butter
1/4 cup organic corn starch
 4 cups milk, divided
1 teaspoon sea salt
pepper to taste

This recipe will make around three cans worth of cream soup.  I haven’t done it before, but I would imagine you could substitute celery for the mushrooms to make cream of celery soup instead.  If you have extra soup that you don’t need, this can be frozen.