Melt butter in skillet over medium heat.
Sauté mushrooms and onion in butter for a few minutes until onions are translucent.
Add salt, pepper and parsley and stir to combine.
Add garlic and sauté about 2 more minutes.
Whisk in flour.
Mixture will be dry.
Begin adding half-and-half about 1/3 cup at a time and stir to incorporate into the flour mixture.
Continue adding the half-and-half stirring and working out all the lumps from the flour mixture until all the milk has been incorporated.
This will take 5-10 minutes to get all the milk incorporated into the flour mixture and lumps worked out so the mixture is smooth.
Bring mixture to a boil (slowly).
Meanwhile, rinse beef under running water (I try to spray water on almost every piece to remove excess salt).
Cut beef in ½”x ½” pieces.
Pull beef apart and try to separate it as much as possible tossing it into the creamy mixture until all the beef has been added.
Stir until thick.
Remove from heat and serve over biscuits, noodles, mashed potatoes or toast.