1 medium red onion, finely chopped
1 tablespoon unsalted butter
1 teaspoon ground coriander
Salt and freshly ground black pepper
⅓ cup oil-packed, sun-dried tomatoes(2.5 ounces), drained and chopped
¼ cup drained capers (1.5 ounces)
6 cornichons
¼ cup tarragon leaves
½ cup flat parsley leaves
1 ½ pounds ground sirloin, chuck or mix
1 tablespoon olive oil
2 ounces Parmesan cheese, thinly sliced with a vegetable peeler
4 large sesame-seed hamburger buns
2 dill pickles, thinly sliced lengthwise with a vegetable peeler
In a small saucepan, combine red onion with butter, coriander and 1 cup water and season with salt and pepper. Bring to a boil, then simmer over medium heat, stirring occasionally, until mixture is reduced to 1/2 cup, about 30 minutes.
Meanwhile, in a small food processor, pulse sun-dried tomatoes with capers, cornichons, tarragon and parsley until finely chopped.
In a medium bowl, lightly mix meat with sun-dried tomato mixture and season with pepper. Shape meat into 4 patties about 3/4 inch thick.
Heat olive oil in a large cast-iron skillet over medium-high heat until just smoking. Add burgers and cook for about 2 minutes on each side for rare or 3 minutes for medium rare. Transfer burgers to a platter and top with Parmesan. Lightly toast buns. Spread a thin layer of onion jam on bottom buns. Top with pickle slices and burgers. Cover with top buns and serve.