Step 1

Place beef chunks and butter on large plate in single layer. Freeze until meat is very firm and starting to harden around edges but still pliable, about 35 minutes.

Step 2

Place one-quarter of meat and one-quarter of butter cubes in food processor and pulse until finely ground into pieces size of rice grains (about 1/32 inch), 15 to 20 pulses, stopping and redistributing meataround bowl as necessary to ensure beef is evenly ground. Transfer meat to baking sheet. Repeat grinding with remaining 3 batches of meat and butter. Spread mixture over sheet and inspect carefully, discarding any long strands of gristle or large chunks of hard meat, fat, or butter.

Step 3

Sprinkle 1 teaspoon pepper and 3/4 teaspoon salt over meat and gently toss with fork to combine. Divide meat into4 balls. Toss each between hands until uniformly but lightly packed. Gently flatten into patties 3/4 inch thick and about 4 1/2 inches in diameter. Using thumb, make 1-inch-wide by 1/4-inch-deep depression in center of each patty. Transfer patties to platter and freeze for 30 to 45 minutes.

Step 4

FOR A CHARCOAL GRILL: Using skewer, poke 12 holes in bottom of disposable pan. Open bottom vent completely and place disposable pan in center of grill. Light large chimney starter filled two-thirds with charcoal briquettes (4 quarts). When top coals are partially covered with ash, pour into disposable pan. Set cooking grate in place, cover, and open lid vent completely. Heat grill until hot, about 5 minutes.

Step 5

FOR A GAS GRILL: Turn all burners to high, cover, and heat grill until hot, about 15 minutes. Leave all burners on high.

Step 6

Clean and oil cooking grate. Season 1 side of patties liberally with salt and pepper. Using spatula, flip patties and season other side. Grill patties (directly over coals if using charcoal), without moving them, until browned and meat easily releases from grill, 4 to 7 minutes. Flip burgers and continue to grill until browned on second side and meat registers 125 degrees for medium-rare or 130 degrees for medium, 4 to 7 minutes longer.

Step 7

Transfer burgers to plate and let rest for 5 minutes. While burgers rest, lightly toast buns on grill, 1 to 2 minutes. Transfer burgers to buns and serve.