In large mixing bowl, combine Stout Beer, vinegar, yellow onions, garlic, tarragon, rosemary, brown sugar and black pepper.  Place steaks on flat surface; sprinkle with Kosher salt.

Place steaks in resealable plastic bag; pour marinade over steaks.  Seal bag and shake until meat is well-coated.  Place bag in large dish and refrigerate 8 hours or up to 24 hours, turning bag 3 to 4 times during marinade process.

Prepare gas or charcoal grill.  When ready to cook, remove steaks from marinade; place on platter and bring to room temperature.  Pour reserved marinade into sauce pan and bring to boil over medium high heat.  Boil sauce for 10 minutes.  Add steak sauce to marinade.

Place steaks on grill and cook, turning, until done throughout, about 5 – 7 minutes.  Baste steaks while cooking with marinade sauce.