Chef John's Grilled Flap Steak

Step 1
Whisk curry paste, fish sauce, rice vinegar, coconut milk, black pepper, cayenne pepper, and salt together in a large shallow glass or ceramic bowl. Add the flap steak and turn to evenly coat. Cover the bowl with plastic wrap and marinate in the refrigerator for 4 to 12 hours.

Step 2
Remove the flap meat from the marinade and shake off excess. Discard remaining marinade.

Step 3
Preheat an outdoor grill for high heat and lightly oil the grate.

Step 4
Cook flap steak on the preheated grill until it starts to firm and is reddish-pink and juicy in the center, 2 to 3 minutes per side. An instant-read thermometer inserted into the center should read 130 degrees F (54 degrees C). Transfer meat to a plate to rest for at least five minutes before slicing against the grain.