Step 1: Rinse the shrimp under cold running water, then drain and blot dry with paper towels. Peel and divide the shrimp. Cut 1 onion into 8 pieces; break each piece into individual layers. Cut the flesh of the whole bell peppers off the cores, and then cut it into 1-inch triangles. Thread the shrimp onto the skewers, alternating with the onion and bell pepper triangles. Arrange the kebabs in a nonreactive baking dish.

Step 2: Prepare the marinade. Cut the remaining onion in quarters. Finely chop the garlic, ginger, onion quarters, diced bell peppers, and jalapeno(s) in a food processor. Add the coconut milk, lime juice, oil, salt, and white pepper. Taste for seasoning, adding salt and pepper as necessary. Add the cilantro and pulse a few times just to mix. Don’t process the marinade too much after the cilantro is added or it will turn green. Alternatively, puree the ingredients in a blender, again adding the cilantro at the end and blending just to mix. Pour the marinade over the kebabs and let marinate for 1 to 2 hours in the refrigerator, covered. (Don’t over-marinate, or the shrimp will toughen.) Turn the kebabs several times to ensure even marinating.

Step 3: Set up the grill for direct grilling and preheat to high. When ready to cook, brush and oil the grill grate.

Step 4: Place the shrimp kebabs on the hot grate and grill until the shrimp is cooked (it will be firm and white), 2 to 3 minutes per side. Baste the shrimp with the butter, if using, during the last 2 minutes of grilling.

Step 5: Serve the shrimp at once with lime wedges. Unskewer the kebabs before eating.