Ingredients

• 2 medium onions, coarsely chopped
• 1 pound crimini or white button mushrooms, trimmed, coarsely chopped
• 2 pounds ground beef (preferably chuck, 20% fat)
• 2 tablespoons low-sodium soy sauce
• 2 teaspoons kosher salt
• 1 teaspoon freshly ground black pepper
• Two (18x13") rimmed baking sheets

Instructions

1. Arrange racks in upper and lower thirds of oven; preheat to 450°F. Pulse onion in a food processor until very finely chopped. Transfer to paper towels and squeeze dry, then transfer to a large bowl.
2. Pulse mushrooms in food processor until very finely chopped. Transfer to paper towels and squeeze dry, then transfer to bowl with onions. (Alternatively, you can finely chop vegetables by hand.)
3. Add beef, soy sauce, salt, and pepper to bowl with onions and mushrooms. Mix well with your hands, then divide into 3-Tbsp.-sized portions and form into patties about 2 1/2" in diameter and 1/2" thick. You should have about 26 patties. Divide between baking sheets.
4. Bake patties 3 minutes, then flip and bake until cooked to desired doneness, 3–4 minutes more for medium/medium-well.
5. Patties can be cooked 3 days ahead; wrap in plastic and chill, or freeze up to 6 months.