They also make a huge difference in a regular cream of mushroom soup. We ran across some beautiful portabellos in the market and decided to work on our mushroom soup recipe. I have never done a side-by-side tasting of portabellos and regular white button mushrooms, but the brown color makes them look like they have more flavor to me, so I use them or crimini.
I suppose their are two choices when making a cream of mushroom soup. It needs to be thickened, which means either a roux of oil and flour or an addition of an egg yolk and cream liaison. For this version I used a roux, some stock, whole milk, and just a soupçon of cream at the end. I also used another one of my secret weapons, a dash of black truffle oil.
Cream of Mushroom Soup
1 oz. dried cepes
2 c. chicken stock
1 yellow onion, coarsely chopped
4 fresh portabello mushrooms, stems removed & reserved
4 T. butter
4 T. flour
2 c. whole milk
1/2 c. heavy cream
1/2 t. black truffle oil
s & p
Heat the chicken stock until warm, add the cepes and let them hydrate for ten minutes. Remove and reserve the cepes. Add the onion and the cleaned stems to the stock and simmer for 30 minutes. Meanwhile, roughly chop the portabello caps and the cepes together and sauté in a mixture of olive oil and butter until they are browned and give up their liquid. Remove and reserve the mushrooms. Heat the butter until bubbling and add the flour, whisking, for just a minute or so. Add the cold milk and strain the stock into the pan and stir. Add salt & pepper, mushrooms, and the dash of truffle oil. Simmer for 30 minutes and taste for seasoning. Now use a food processor or immersion blender to puree the soup. Add the cream and gently reheat to a simmer and serve. Should make 4 one-cup servings.