TO MAKE CARAMELIZED ONIONS: In rondo over medium heat, melt butter. Add onions and sautè until caramelized, stirring often. Add garlic and sautè 1 minute. Stir in vinegar. Cool and cover. (Yield: about 1 lb., 8 oz.)
FOR CREOLE MUSTARD AIOLI: In bowl, mix mayonnaise, Creole-style mustard and garlic. Cover and refrigerate.
FOR EACH SERVING, TO ORDER: Grill 1 steak to medium. Season with 1/2 tsp. salt and 1/4 tsp. pepper. Slice 4 oz. steak thinly at an angle across the grain. Cover and reserve the remaining steak.
Spread 1 Tbsp. Creole mustard aioli on each cut side of bread. Top bottom bread half with 1 oz. blue cheese, the warm steak slices, 1 oz. caramelized onions, 1/4 oz. spinach leaves and other bread half. Plate and serve.
Recipe and photo above submitted by the Cattlemen's Beef Board and National Cattlemen's Beef