Combine butter, lemon juice, pepper flakes, garlic, and salt in pan. Cook over hot side of grill, stirring occasionally, until butter melts, about 1 1/2 minutes; transfer to cooler side of grill and proceed to grill shrimp, adding parsley just before serving.

URL: http://www.cooksillustrated.com/recipes/detail.asp?docid=7686

Makes enough to sauce 1 1/2 pounds shrimp.