There's something inherently comforting and nostalgic about a juicy, grilled burger on Memorial Day. But who says comfort food can't have a touch of gourmet flair? In this third installment of our Memorial Day series, we'll elevate your burger game with unique flavors, topping ideas, and a recipe that will make your backyard gathering a culinary triumph.

Ingredients:

For the Burgers:

1. 2 pounds of ground beef (80% lean, 20% fat)
2. Salt and pepper to taste
3. 4 brioche burger buns

For the Toppings:

1. Blue Cheese and Caramelized Onions: Blue cheese crumbles, 2 large onions (thinly sliced), 2 tablespoons butter, 1 tablespoon brown sugar, and 2 tablespoons balsamic vinegar.
2. Spicy Southwest: Pepper jack cheese, 1 avocado (sliced), fresh salsa, and jalapenos.
3. Portobello and Swiss: Swiss cheese and 2 large portobello mushrooms (sliced and sautéed).
4. Gourmet Veggie: Goat cheese, arugula, roasted red bell pepper, and basil pesto.

Instructions:

1. Preheat your grill to medium-high heat.
2. Form the ground beef into 4 equal patties, about 3/4 inch thick. Season both sides of each patty with salt and pepper.
3. Grill the burgers for about 4-5 minutes on each side for medium doneness. Adjust the timing to your desired doneness.
4. In the last minute of grilling, add the respective cheeses to each burger and close the grill to allow the cheese to melt.
5. While the burgers are grilling, prepare your toppings. For caramelized onions, sauté onions in butter over medium heat, stirring occasionally, until golden brown and softened. Add the brown sugar and balsamic vinegar, and cook for an additional 2-3 minutes until the onions are caramelized.
6. Once the burgers and toppings are ready, assemble the burgers on the brioche buns with your choice of unique toppings. 
7. Serve the burgers with your favorite sides, such as potato salad, coleslaw, or grilled corn on the cob.

Tips for the Perfect Burger:

1. Don’t overwork the meat: When forming the patties, try to handle the meat as little as possible to prevent the burgers from becoming tough.
2. Indent the middle: Press a small indentation in the center of each patty before grilling. Burgers puff up in the middle as they cook, and this trick will ensure a uniformly flat burger.
3. Let them rest: After removing the burgers from the grill, let them rest for a few minutes before serving. This allows the juices to redistribute throughout the burger.

With these tips and recipes at hand, you can look forward to a Memorial Day filled with not just classic, but creatively tantalizing burgers. Happy grilling!