Sauté the white onions in the butter over high heat.
In about 3 minutes the onions will begin to turn brown.
Add 1 cup of the beef stock to the onions.
Also add the pepper and garlic at this time.
Continue to simmer over medium high heat until the sauce has reduced by about half.
Add the whiskey, green onion, and remaining 1 cup of beef stock to the sauce and let it simmer over low heat while you prepare the steaks.
When your steaks are just about done, combine the cornstarch with the tablespoon of water in a small bowl.
Stir just until the cornstarch dissolves.
Remove the whiskey sauce from the heat and add the cornstarch to it.
Put the sauce back on the heat and continue to cook on low until the sauce has thickened to the consistency you desire.
Serve the steak covered with the sauce.