I'm not sure where this came from and my mom doesn't remember either. I've tried varying the recipe; adding garlic, fresh ground pepper. Nothing is as good or as simple as the original recipe. —Brooksie
In a shallow casserole dish, unfold the flank steak and cover both sides very liberally with dried Thyme ( approx 2-3 tablespoons per side). Pour entire bottle of Soy Sauce over the thyme covered steak. Let the steak sit in the soy sauce marinade for at least 1/2 hour and no more than an hour, turning it over once. (The thyme will not all stick to the steak but will continue to flavor the marinade)
Preheat either a grill or prepare to use the broiler.
Remove the steak from the marinade and either grill or broil the steak for approx 4-5 minutes per side for medium rare.
After removing from the grill or broiler, allow the steak to sit for at least 5-10 minutes before slicing diagonally against the grain.