For the Marinade
1 cup ketchup
1/2 cup Coca-Cola or water (see note)
1/2 cup sugar
1/2 cup extra virgin olive oil
1/4 cup red wine vinegar
1/2 cup Worcestershire sauce
1/2 cup A-1 Sauce
1 1/3 tablespoons freshly ground black pepper
2 pounds sirloin or rib eye trimmed and cut into large cuts as big as 2 to 3 inches square
1 large onion, cut into thick strips vertically
1 tablespoon butter
1 tablespoon extra-virgin olive oil
1 teaspoon salt
1/2 teaspoon freshly ground black pepper
1 teaspoon sugar
In a medium sauce pan, place all marinade ingredients and bring to a boil, then reduce heat and gently simmer for 5 minutes. Remove from heat and cool completely.
Trim any gristle or large pieces of fat from beef. Cut into large pieces; about 2-3 inches square. Place cut beef in a zip lock bag. Pour cooled marinade over beef, seal and marinate 8-24 hours.
In a medium sauté pan over low heat melt butter in olive oil and place onions, salt, pepper and sugar and cook stirring occasionally for 30-40 minutes until onions are caramelized but not cooked down too much. Start cooking tips as the onions get close to finishing.
When you are ready to grill, drain all marinade and heat a ribbed grill pan over extremely high heat or heat your outdoor BBQ grill to the highest setting.
Lightly oil or spray pan or grill and place beef onto grill or pan not touching each other and cook untouched for 2-3 minutes (Depending on how thick they are and how hot your grill or stove gets, the timing will need to be monitored). If you are not certain, cut into one and check for doneness. Turn once and cook for another 1-2 minutes for medium rare.
Remove to a platter and serve with the caramelized onions.