Pound the meat between two layers of plastic wrap until it’s thin and even 

Dredge the meat in flour

Melt butter in pan over medium heat, add steaks and cook to medium rare, typically about 2 minutes per side

Remove meat from pan

Add mushrooms and onions to the pan and stir a few minutes until they start to soften (add another tablespoon or two of butter if needed)

Lower heat a notch and add the 2 T flour and cook another 2 minutes, stirring constantly

Whisk the stock in slowly and let it simmer 5 minutes or so 

Turn off heat, add cream, mixing thoroughly

Serve sauce over the steaks