Melt a couple tbsp of butter in a frying pan and add the onion and mushrooms. Saute until the onions are soft and the mushrooms have shrunk down.
Transfer to a sauce pan. Deglaze the pan with a splash of the stock and add that to the pot as well.
Start cooking the "steaks" in the frying pan at this point.
Add the stock and spices and whisk to blend.
Bring to a simmer.
Add thickening agent of choice, adjust S&P to desired amount.