Step 1: Prepare Caramelized Onions

Start by preheating a large skillet over medium heat. Add 2 tablespoons of unsalted butter and 2 tablespoons of olive oil, allowing the mixture to heat up until the butter melts completely. The combination of butter for rich flavor and olive oil for a higher smoke point prevents burning during cooking.​​

Once hot, toss in the 2 large yellow onions, thinly sliced into half-moon shapes. Season immediately with salt, pepper to taste, and 1 teaspoon of granulated sugar. Stir everything well with a wooden spoon to separate the onion slices and coat them evenly. Cook on medium-high initially, then reduce to medium after a few minutes.​​

Let the onions cook undisturbed for about 8 to 10 minutes, stirring occasionally. They will soften, turn golden, and develop a deep caramelized color as the sugar enhances their natural sweetness. Move the skillet to the back of the stove if needed to free up space for the burgers. Turn off the heat once perfect, keeping them warm. This step builds layers of flavor that elevate the entire burger.​​

Step 2: Mix Burger Patties

While onions cook, finely chop 4 tablespoons of fresh parsley and mince 4 cloves of garlic. Use a sharp knife for uniform pieces that distribute evenly. In a large mixing bowl, combine these with 2 ¼ pounds of 85/15 ground beef, 2 tablespoons of salt-free steak seasoning, and about 1 tablespoon of Worcestershire sauce. Add a pinch of salt if desired.​​

Mix gently with your hands, working quickly to avoid overworking the meat. Overmixing compacts the beef, leading to dense burgers. The salt-free seasoning prevents oversalting, as pre-blended spices often contain excess sodium. Divide the mixture into 8 equal portions for small patties.​​

Step 3: Shape the Patties

Take each portion of beef mixture and form it into a patty about ½-inch thick. Press a deep indentation in the center of each using your thumb or a spoon. This thumbprint technique counters puffing during cooking, ensuring flat, even burgers that fit perfectly on the buns. Aim for thin patties, as they shrink significantly when grilled.​​

Place shaped patties on a plate or tray, ready for the grill pan. Handle minimally to preserve juiciness from the 15% fat content in the 85/15 beef, which provides ideal moisture without greasiness. Refrigerate briefly if not cooking immediately.​

Step 4: Preheat Grill Pan and Cook Patties

Preheat your grill pan over medium to medium-high heat. Drizzle lightly with oil to prevent sticking. Arrange the patties on the hot surface, giving space between them. Sear for 3 to 4 minutes per side for medium doneness, flipping once. Adjust time: 4 to 5 minutes per side for well-done.​​

The grill pan creates appealing sear marks and locks in juices. Listen for a good sizzle upon contact, indicating proper heat. Avoid pressing down, as this squeezes out moisture. Internal temperature should reach 160°F for safety, though Laura prefers medium.​​

Step 5: Add Cheese and Melt

Two minutes before patties finish, top each with shredded Gruyere cheese, about 1 ounce per burger. Tent loosely with aluminum foil to trap heat and melt the cheese smoothly without direct flame. The nutty, creamy Gruyere complements the savory beef perfectly.​​

Remove from heat once cheese bubbles and patties reach desired doneness. Let rest briefly under the foil tent, allowing juices to redistribute for maximum tenderness. This resting mimics professional techniques for superior texture.​

Step 6: Prepare Buns and Sauce

Slice 8 small Kaiser rolls horizontally. Mix mayonnaise and whole grain mustard in a small bowl, using a thin layer ratio for tangy creaminess. Spread lightly on the cut sides of the bottom buns. Coarse mustard adds texture and bite that pairs with sweet onions.​​

Season fresh tomato slices and lettuce leaves with salt and pepper. Crisp romaine or iceberg provides crunch and holds toppings securely. Keep assembly line ready for quick building.​

Step 7: Assemble the Burgers

Place a cheese-topped patty on each sauced bottom bun. Pile on a generous spoonful of caramelized onions, letting their sweetness shine. Add tomato slices, then lettuce to contain juices. Cap with top buns.​​

Serve immediately with napkins, as juices may drip. Cutting one in half reveals the perfect layers: juicy beef, melted cheese, sweet onions, and fresh veggies.​