Sep 1, This gourmet grilled cheese is loaded with herbed caramelized onions, gooey Gruyere and white cheddar cheeses, and is cooked in a savory rosemary butter! One bite of this ultra savory and gourmet grilled cheese, and you’ll never want a regular grilled cheese again!. Ingredients. Butter; 4 slices country white sourdough bread, cut on deep diagonal into 1/3-inch-thick slices (each about 7x3 1/2 inches); 4 thin slices prosciutto. Sep 15, Why am I calling these ultimate? First off, I love grilled cheese sandwiches. There are endless combinations, and honestly, since I love cheese. Make and share this The Ultimate Grilled Cheese Sandwich recipe from Genius Kitchen. There is no denying it, this is truly the Ultimate Grilled Cheese Sandwich. You see, when we made it, this dish disappeared so fast in our Test Kitchen it barely. With only 3 simple ingredients, this truly is the ultimate grilled cheese. Perfect for a tight budget or someone who's short on time, this.