1In a large bowl, using a fork, combine the meats, Worcestershire sauce, egg yolks, salt and pepper. Mix, but try not to overwork the meats. Lightly form very thin hamburger patties. Press a slice of butter (approx. 1/2 tablespoon) into the center of the patty. Top with another thin hamburger patty and press the edges of the patties to seal tightly. Continue until all patties are made. Place on a heated grill. Cook the hamburgers 4 minutes on one side, turn and cook an additional 6 minutes, until a thermometer placed in the center of the burger reads 160° F. In the meantime, grill the hamburger rolls, cut side down, for a minute or two until toasted. Place a hamburger patty and a thick slice of blue cheese on each bun, and top with arugula and sliced tomato.