what can I substitute for canned cream of mushroom soup concentrate?

Pageen's recipe looks wonderful and will, I'm sure, do a great job. Here's another recipe that I've used for many years that seems to work fine - It can be adjusted for cream of chicken, cream of mushroom or other cream soup concentrates:

2 Tablespoon salted butter
3 Tablespoons all-purpose flour
1/2 cup chicken/beef/pork/lamb broth or stock (or an extra 1/2 cup
of milk)
1/2 cup milk (2% is okay)
Additions appropriate to the type of cream soup needed:
1/2 cup sliced/chopped mushrooms, sautéed in butter
1/4 cup chopped chicken/pork/beef/seafood (as appropriate)
1/2 cup frozen/thawed/drained spinach
Salt and pepper to taste

In a saucepan over medium-high heat, melt the butter. Whisk in the flour, and keep whisking until smooth and bubbly. Remove the pan from the heat and, whisking rapidly and constantly, add the broth and milk a little at a time. Once the mixture is smooth, add any additions and return to the pan to the heat. Bring the sauce to a gentle boil. Cook, stirring constantly, until it thickens. Taste and add salt and pepper as needed.

Makes about 1 1/2 cups

This is the same idea as jsdunbar's above... This is a mushroom cream sauce I use in place of canned soups. Depending on the rest of the recipe you're working with, you can adjust the thickness of the sauce by diluting with more cream, broth or water.

3 tablespoons unsalted butter
1 pound white button mushrooms. Break off stems and wipe clean with a damp paper towel. Break into 1/2-inch pieces.
3 medium cloves garlic, minced or pressed through garlic press (about 1 tablespoon)
3/4 teaspoon salt
1/8 teaspoon ground black pepper
3 tablespoons unbleached all-purpose flour
1-1/2 cups low sodium chicken broth
1-1/2 cups heavy cream

In a heavy saucepan or Dutch oven, melt butter over medium-high heat until foaming stops. Add mushrooms, garlic, salt, pepper. Let mushrooms cook about 5 minutes or a little longer, stirring occasionally to prevent sticking, until their moisture is released and liquid has evaporated. Add flour and cook for 1 minute, stirring constantly. Stir in broth and bring to simmer, stirring constantly. Add cream, reduce heat to medium, and simmer for 10-12 minutes until sauce thickens and reduces to about 3-1/2 cups. If you want to thin the sauce, add cream, broth or water in small amounts until you have the consistency you want. Wait until combining sauce with rest of dish before adding more salt or pepper.

I use a thick white sauce to do the same thing. I add flavour by adding herbs or wine, or starting with chopped onions & sautéing them, adding chopped celery, mushrooms or whatever, then the four. Stir for a moment then slowly add milk, stirring constantly to make, in effect, a small amount of thick cream soup. It works well for me & doesn't take long.