1 turkey thigh , about 2 pounds, skinned and boned (or 1 1/2 pounds skinless, boneless thighs) cut into 1-inch chunks; arranged on sheet pan; frozen until semifirm, about 30 minutes
1/2 teaspoon table salt
1/2 teaspoon ground black pepper
2 teaspoons Worcestershire sauce
2 teaspoons Dijon mustard
1 tablespoon vegetable oil or canola oil
1. Working in 3 batches, place semifrozen turkey chunks in workbowl of food processor fitted with steel blade; pulse until largest pieces are no bigger than 1/8-inch (see illustration 4), 12 to 14 one-second pulses.
2. Transfer ground meat to medium bowl. Stir in salt, pepper, Worcestershire sauce, and mustard until blended, and divide meat into 4 portions. Following illustration 5, lightly toss one portion from hand to hand to form a ball, then lightly flatten ball with fingertips into 1-inch-thick patty. Repeat with remaining portions.
3a. To Cook Indoors: Heat a large, heavy skillet (preferably cast-iron or stainless steel with an aluminum core) over medium heat until very hot, 4 to 5 minutes. Swirl oil in pan to coat bottom, then add burgers. Cook over medium heat without moving burgers until bottom side of each is dark brown and crusted, about 5 minutes. Turn burgers over; continue to cook until bottom side is light brown but not yet crusted, 4 to 5 minutes longer. Reduce heat to low, position cover slightly ajar on pan to allow steam to escape, and continue to cook 5 to 6 minutes longer or until center is completely opaque yet still juicy, or an instant-read thermometer inserted from the side of the burger into the center registers 160 degrees. Remove from pan and serve immediately.
3b. To Grill: Alternatively, grill burgers over medium-low fire (you can hold your hand about 5 inches above grill surface for 5 seconds) until dark spotty brown on bottom side, 7 to 9 minutes. Turn burgers over; continue grilling 7 to 9 minutes longer or until bottom side is dark spotty brown and center is completely cooked or instant-read thermometer registers 160 degrees. Remove from grill and serve immediately.