In a large deep saucepan, heat the oil to 375°. Spread the remaining 1 cup cornstarch on a large plate. Working with 2 at a time, remove the crabs from the marinade and dredge them in the cornstarch, shaking off any excess. Using tongs, add the crabs to the hot oil and fry, turning once, until cooked through and very crisp, about 4 minutes. Transfer the crabs to a rack to drain.