Step 1

Bring vinegar, soy sauce, fish sauce, sugar, and garlic to a simmer in a small saucepan over medium-high heat. Reduce heat and gently simmer until reduced by about half (it will still be fairly loose and won’t yet coat a spoon), 6–8 minutes. Set sauce aside.

Step 2

Prepare a grill for high indirect heat (for a charcoal grill, bank coals on one side of grill; for a gas grill, leave one or two burners off); oil grate with vegetable oil. Season steak generously with kosher salt. Grill over direct heat, turning every minute, until deeply browned on all sides (including standing it on its side with tongs to render fat cap), 6–8 minutes.

Step 3

Move steak over indirect heat and grill, turning every 1–2 minutes and moving closer to or farther away from heat as needed to build even color, until an instant-read thermometer inserted into the thickest part of steak registers 100°, 10–12 minutes. Start basting steak. Continue to grill, turning and basting with a light coating of sauce and moving closer to or farther away from heat as needed to create a deep crust on steak without scorching, until very dark brown and thermometer registers 120° for medium-rare (internal temperature should climb to about 130° as steak rests), about 10 minutes. Transfer steak to a wire rack set inside a rimmed baking sheet and let rest 15–30 minutes.

Step 4

Transfer steak to a cutting board and slice into thick strips. Arrange on a platter; drizzle with olive oil and sprinkle with sea salt. Serve with lemon wedges.