In a medium size bowl, whisk together bourbon, brown sugar, worcestershire and soy sauce. Pour into a large zip-top bag; add onion and steak. Seal, squeezing to expel any air, and let meat marinate at least 2 hours, up to overnight (or freeze up to 3 months).
Steak tips:
When ready to cook, defrost steak and onions if you previously froze them. Drain and season with salt and pepper.
Set up your grill for direct high heat. To grill meat, sear on one side until nicely browned, 4 to 6 minutes. Turn meat and grill until it reaches desired doneness.
Cook onions in a grill pan, stirring occasionally, until golden, about 10 minutes. Or cook onions directly on grill grates asway from direct heat, carefully turning once, for 8 to 10 minutes.
Alternate procedure:
Whisk 2 tablespoons packed light brown sugar and 2 tablespoons bourbon together in a small bowl. Coarsely chop until you have 1/4 cup fresh parsley leaves. Cut 2 pounds New York strip steak into 1-inch cubes, then season them with 1/2 teaspoon kosher salt.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat until shimmering. Add the steak cubes and sear until browned, flipping them halfway through, 6 to 8 minutes total. Add the brown sugar and bourbon mixture and cook for 1 minute more. Remove from the heat and garnish with the parsley.