Sauce
2 Tbsp. balsamic vinegar
2 Tbsp. Worcestershire sauce
2 Tbsp. ketchup
1 Tbsp. extra-virgin olive oil
1 Tbsp. vinegar-based hot sauce (such as Frank’s or Crystal)
1 tsp. Dijon mustard
1 tsp. honey
Kosher salt
Steak and Assembly
Vegetable oil (for grill)
1½ lb. skirt steak, cut into 4"–5" pieces
Kosher salt, freshly ground pepper
Flaky sea salt
Sauce
Whisk vinegar, Worcestershire sauce, ketchup, oil, hot sauce, mustard, honey, and 1 Tbsp. water in a medium bowl to combine; season with salt.
Do ahead: Sauce can be made 2 months ahead. Store airtight at room temperature.
Steak and Assembly
Prepare a grill for medium-high heat; oil grate. Season steak generously with kosher salt and pepper. Grill, turning every 1–2 minutes and moving closer to or farther away from heat as needed to build even color, until nicely charred and an instant-read thermometer inserted into the thickest part of steak registers 125°(juices pooling on top of meat is a fairly good indicator that meat has reached medium-rare), 7–9 minutes. Transfer steaks to a cutting board and let rest 5–10 minutes before slicing against the grain.
Transfer steak to plates and top with sauce. Crack some pepper over and sprinkle with sea salt.