1/2 cup soy sauce
1/3 cup bourbon (or other whiskey)
1/3 cup firmly packed dark brown sugar
1 tablespoon Dijon mustard
1 teaspoon hot sauce
1 1/2 to 2 lb flank steak
Whisk the soy sauce, bourbon, brown sugar, mustard, and hot sauce together in a small bowl until the sugar dissolves. Pour the ingredients into a resealable plastic bag, and add the steak. Let the steak marinate for at least 20 minutes or pop it in the fridge for up to 2 hours before grilling. Return the steak to room temperature before grilling.
Preheat your grill to medium-high heat. Oil the grates lightly (I use the tongs to hold a paper towel that’s been dipped in oil and rub it over the grates).
When the grill is hot, remove the steak from the marinade, shaking off excess (no need to pat the steak dry). Set the marinade aside, don’t throw it away. Grill the steak for 4-5 minutes per side, or until cooked to your desired doneness (the cooking time is going to depend on how thick your steak is, how hot your grill is, etc. I use an instant read thermometer to test the temperature for best results). Transfer the steak to a cutting board, tent with foil, and allow to rest for at least 5 minutes.
While the steak is resting, pour the marinade into a small saucepan. Bring to a boil and cook until reduced and syrupy. Slice the steak thinly across the grain and serve with the sauce.