Melt butter in a 3-quart saucepan over medium heat until fragrant and bubbly. Add mushrooms, peppers, onions, and cook, stirring occasionally until tender, about 5 minutes.
Stir in gluten free flour and cook for 1 minute. Cooking the flour keeps your soup from tasting like raw flour.
Turn off the flame and whisk the milk in. Turn the flame back on and cook, whisking, until the soup comes to a boil and is thickened, about 10 minutes. The mixture will thicken as it heats. Just keep stirring over medium low heat. Make sure to scrape the bottom of the pot so the flour doesn't stick.
Add parsley, and season with salt and pepper.
Serve garnished with parsley and shredded cheese if you like. Or save in your fridge to use as an ingredient in a casserole or skillet meal.
I love to just slice my mushrooms to keep their meaty texture. However, if you prefer, you can cut up your mushrooms into bite-size pieces.
Can you use different types of mushrooms? Yes. I used button mushrooms for this recipe. You can go with cremini mushrooms or even shiitake or porcini mushrooms if you prefer.
Need to make the soup dairy-free? No problem. I haven't tried this myself, but instead of butter, use a dairy-free butter substitute like Earth Balance. And there's no reason why you can't go with a lactose-free milk, unsweetened plain almond milk, or coconut milk.
There are a few add-ins you could choose. How about chopped bacon, bite-size cooked chicken or turkey, or cooked, diced potatoes? It’s up to you.