Garlic-Herb Chuck Burgers with Balsamic Onions

Steps

1. Freeze the beef chuck cubes for 10 minutes until firm at the edges.
2. Meanwhile, heat half the olive oil in a large skillet over medium heat. Add the onion and cook, stirring often, until soft and golden, about 12 minutes.
3. Stir the balsamic into the onion and cook 1 minute until glossy; transfer to a bowl and wipe out the skillet.
4. Pulse the chilled beef chuck in a food processor in two batches until coarsely ground; do not overprocess.
5. In a bowl, gently mix the ground chuck with the garlic, thyme, Worcestershire sauce, half the salt and the black pepper. Form 4 patties about 3/4 inch thick with a slight dimple in the center.
6. Sprinkle the patties with the remaining half of the salt.
7. Heat the remaining half of the olive oil in the skillet over medium-high heat. Cook the patties 4 to 5 minutes per side until they reach 160°F (71°C) in the center. Rest 2 minutes.
8. Toast the whole-wheat bread slices.
9. Build each burger on a slice of toast: romaine, a patty, tomato slices and balsamic onions, then top with a second slice.