Ingredients Meat & Poultry Beef Recipes Ground Beef Recipes Bistro Burgers By Lauryn Tyrell Lauryn Tyrell Website Lauryn is the senior food editor for Martha Stewart Living. Editorial Guidelines Updated on May 19, 2021 Print Share Share Tweet Pin Email Photo: Con Poulos Prep Time: 35 mins Total Time: 40 mins Servings: 4 A few simple moves can elevate a backyard hamburger to steak-house status. Grilled onions, a swipe of Dijon over the patties before grilling, and toasted brioche buns are just a sampling of some of the high-end embellishments you can expect with your burger tonight. Ingredients ⅓ cup mayonnaise 3 tablespoons Dijon mustard 2 tablespoons freshly grated horseradish Kosher salt and freshly ground pepper 1 ½ pounds ground beef (85 percent lean) 4 brioche buns, split Vegetable oil, for drizzling and grill 1 large sweet onion, such as Vidalia (12 ounces), sliced into ½-inch-thick rounds 2 tablespoons Worcestershire sauce 4 slices sharp white cheddar 2 beefsteak tomatoes, sliced into thick rounds Flaky sea salt, such as Jacobsen Mixed greens, such as watercress and chopped radicchio, and cornichons, for serving Directions Stir together mayonnaise, 1 tablespoon mustard, and horseradish. Season lightly with salt and pepper. Form beef into 4 patties, each slightly larger in circumference than buns. Make a small indent in center of each patty with your thumb (to keep them from puffing up on the grill). Cover loosely and refrigerate until ready to cook. Heat grill to medium-high, and place a large straight-sided skillet with a lid nearby. Brush grates with oil. Drizzle onions lightly with oil; season with salt and pepper. Grill, flipping once, until well charred and crisp-tender (they should still maintain a bit of crunch), 7 to 9 minutes. Transfer to skillet, drizzle with Worcestershire sauce, and cover with lid. Cover grill and return to medium-high heat. Generously season indented sides of patties with salt and pepper. Brush with remaining 2 tablespoons mustard. Brush grates with oil. Place patties on grill, indented-sides down, and generously season other sides. Cook until lightly charred, 3 to 4 minutes. Flip patties, top each with cheese, and cover grill. Continue to cook, moving occasionally as needed to avoid flare-ups, until cheese has melted and burgers are cooked through, 3 to 4 minutes more. Transfer to skillet; cover with lid. Grill buns, cut-sides down, until lightly toasted, about 1 minute. Sprinkle tomatoes with flaky salt. Spread both sides of buns with horseradish mixture, then add patties, onions, and greens. Serve, with salted tomatoes and cornichons alongside. Cook's Notes Transferring the onions and patties to a covered skillet as they come off the grill keeps them warm and juicy. Print