Add butter, onions, and mushrooms to saucepan and sauté until onions are soft and translucent. Add 1 TBSP flour, mix, then set aside.
In the same pot, add the chicken broth bringing it to boil, then stir in the cream, and TBSP of flour, with seasonings. Heat to thicken
In a food processor, add the mushrooms/onion mix, and the broth/cream mix, and pulse until smooth
Return to pot, allowing to boil mixing occasionally.
Serve and garnish with croutons or parsley