Prepare the crabs, take of the main shell, take off the claws and cut the legs into two pieces.
For the sauce, in a very hot wok, fry the garlic and ginger in a little oil. About 1 min, don't let the garlic burn.
Put all the ingredients for the sauce (except the cornstarch) in the wok and stir, lower the heat.
Mix the cornstarch in a few tablespoons of water to form a runny liquid. Add a few tablespoons to the sauce to thicken it. It should become a bit more gluey to adhere to the crabs.
When the right consistency has been reached, adjust seasoning to taste.
Add the crabs and coat with the sauce. If raw, cook this until the crabs change colour and is cooked through about 7 minutes. If cooked, then cook until the crabs are warmed through.
Dish it all out onto one big serving platter. Sprinkle on some spring onions for colour.
Serve hot with slices of toast or steamed rice.