1 tablespoon olive oil, divided
1 pound 90 percent lean ground beef
2 cups thinly sliced shallots
1/2 cup shredded sharp cheddar cheese
1/2 teaspoon kosher salt, divided
1 cup arugula
1 tablespoon white wine vinegar
4 hamburger buns toasted
2 cloves garlic, minced
3 tablespoons light mayonnaise
1. Heat a nonstick skillet over medium-low heat. Add 2 teaspoons oil; swirl to coat. Add shallots and 1 ⁄4 teaspoon salt; cook 15 minutes or until golden brown, stirring occasionally. Stir in vinegar; cook 1 minute. Remove from heat; keep warm.
2. Gently combine garlic and beef. Divide meat mixture into 4 equal portions, gently shaping each into a 1 ⁄2 -inch-thick patty. Press thumb in centre of each patty, leaving a nickel-sized indentation. Sprinkle evenly with 1 ⁄4 teaspoon salt.
3. Heat a large cast-iron skillet over medium-high heat. Add 1 teaspoon oil to pan; swirl to coat. Add patties, and cook 3 minutes on each side or until desired degree of doneness. Top each patty with 2 tablespoons cheese; cover until cheese melts.
4. Place 1 ⁄4 cup arugula on bottom half of each bun; top with 1 patty and one-fourth of shallot mixture. Spread about 2 teaspoons mayonnaise on cut side of top half of each bun; place on top of burgers.