With a melon baller, scrape thin slices of coconut from shells until only 1/4-inch rim remains. Use flesh to make coconut stock as described in recipe below. Trim ends of shells so they stand on end.
Preheat broiler. Warm scraped coconut shells in oven. Heat clarified butter in pan. Add garlic, then shrimp. Season with salt and pepper and cook for 3 minutes. Add onion and cook 2 minutes more.
Pour off excess butter from pan and add soy sauce. Stir in coconut fat. When melted, add stock and bring to a boil. Add dissolved arrowroot to pan to thicken sauce. Remove from heat and fill warmed coconut shells. Decorate shrimp with remaining coconut shavings and broil for 1 1/2 minutes. Serve immediately.
Place coconut shavings in bowl and pour water on top. Cover and set aside for 30 minutes. Strain through cheesecloth and cool. Skim coconut fat and reserve.