Step 1

In a medium bowl, whisk together 4 tablespoons of gochujang, the soy sauce, sesame oil and grapeseed oil. Measure 2 tablespoons of the mixture into another medium bowl and set aside. Add the shrimp to the remaining mixture and toss to coat, then cover and refrigerate for at least 30 minutes or up to 1 hour.

Step 2

To the reserved 2 tablespoons gochujang mixture, whisk in the remaining 1 tablespoon gochujang and the rice vinegar, then toss in the butter; set aside.

Step 3

Prepare a charcoal or gas grill for high-heat cooking. For a charcoal grill, ignite a large chimney of coals, let burn until lightly ashed over, then distribute the coals evenly over one side of the grill bed; open the bottom grill vents. For a gas grill, turn all burners to high. Heat the grill, covered, for 5 to 10 minutes; clean and oil the grate.

Step 4

While the grill heats, thread the shrimp onto four or five 12-inch skewers, dividing them evenly; skewer each shrimp in a C shape, piercing through two points. Place the skewers on the hot side of the grill and cook until they begin to char and the tails begin to blister, 2 to 3 minutes. Flip and continue to cook until the shrimp are just opaque, another 1 to 2 minutes.

Step 5

Slide the shrimp off the skewers into the bowl containing the gochujang-butter mixture and toss until the butter has melted and the shrimp are well coated. Add the scallions and toss again, then taste and season with salt and pepper.