Combine all ingredients for sauce and mix well.
Prep crabs by removing face, gills and abdominal flap. Cut in half vertically.
Heat a large wok or high sided pan on high heat, add ~⅛” of oil to the pan. Lightly dredge the crabs in corn starch and shake off excess. Fry in hot oil for 2 minutes. Flip crabs using a spatula. The shells should be bright red. There will be some starch stuck to the pan, use a metal spatula to scrape loose. Cook for 2 more minutes.
Add ginger, scallions and jalapeno to the pan with the crab. Stir and cook for ~2 minutes until very fragrant.
Pour sauce over everything in the pan. Stir until evenly coated.
Serve immediately.