If there is an excess of fat in the pan remove, if there is a lack add 1 tbsp butter and the olive oil. Foam out the butter, over medium heat
Add the onion and mushroom, sauté until the onions are translucent, and the mushrooms begin to take color
Deglaze the pan with the wine, scraping the pan to dissolve the fond. Reduce by half.
Add the stock, and reduce once again
Remove from heat, stir in the cream, allow the residual heat to thicken the sauce, if necessary return to low heat, stirring frequently.
Remove from heat, and mount the last pat of butter, Taste, Season and Balance.
Plate the protein on a bed of gravy and cover with sauce.