Pour 1 cup of beef stock into a pan and boil until reduced to 1/2 cup and slightly thickened. Set aside.
With the back of a spoon spread mustard thinly over one side of each steak. Cover with ground pepper and a pinch of salt, pressing lightly into each steak. Flip over and repeat on other side. Watch the quantity of salt if not using low sodium beef broth.
Clean and slice mushrooms and set aside. Snip and ready fresh herbs. Mince the garlic clove. Set aside.
Heat a pan until very hot and add the olive oil. Fry steaks for 2 to 2 1/2 minutes per side (medium rare). A dark crust will form so treat gingerly, so as not to lose too much crust when turning or transferring. Transfer steaks to a warm plate and cover with foil to keep warm.
In a separate pan, brown the mushrooms and garlic in butter with herbs and a small amount of pepper & salt. When mushrooms are golden, add in 4 tablespoons of whisky. (You may want to have a pot lid handy, in case the alcohol ignites in the hot pan...just cover it).
Quickly add the 1/2 cup condensed beef broth, 1/2 cup of cream & 1/2 tsp. mustard. Cook the sauce down until it has a thick gravy consistency.
Pour over each steak and garnish with parsley. Great with a side of roasted potatoes.