To prepare your crabs humanely, place them in the freezer for 1 hour to put them to sleep.
For the Sate Sauce: Pour the vegetable oil in a wok and bring to medium heat, fry the garlic and spring onions until fragrant. Now add the crab meat, shrimp, sugar, salt, oyster sauce, and fish sauce. Stir to incorporate, and then reduce the heat to a low simmer for 30 minutes, stirring every 5 minutes. Lastly add the chile oil, stir and simmer for another 5 minutes.
Cooks Note: Use this sate sauce as a dipping sauce for noodle soups or add to stir-frys. Refrigerate the extra sauce in an airtight container.
For the crab: Remove the upper shell of the crab, pick off the gills, which look like little fingers, and discard them. Clean the crab under running water and drain. Place the crab on its stomach and chop the crab in half with a heavy cleaver. Now chop each half into 4 pieces, chopping each piece after each leg. With the back of the cleaver gently crack each claw this makes it easier to extract the meat.
Heat the oil in a wok to 400 degrees F, or until a cube of bread dropped into the oil browns in 5 seconds. Dust the crab pieces with potato starch, shaking off the excess. Deep-fry the crab in batches for 3 minutes, turning over once, until golden brown. Remove the crab pieces from the wok and drain on kitchen paper towels. Carefully, remove the oil from the wok, reserving 2 tablespoons, and clean the wok.
Heat the reserved oil in the wok, then add the shallots and garlic and fry until fragrant. Now add the sate sauce and stir for 1 minute. Add the crab, spring onions, and chiles and toss, making sure to coat the crab well. Transfer the mixture to a serving bowl and garnish with red chile.
Serve the dish with jasmine rice.