Singaporean Chili Crab

Name: Singaporean Chili Crab
Ingredients: 1 tablespoon belacan shrimp paste; 2 whole large Dungeness crabs, cleaned and scrubbed; 6 fresh red chiles; One 1-inch knob ginger, peeled; 2 shallots, roughly chopped; 4 garlic cloves, peeled; 1 cup plus 3 tablespoons cornstarch; Neutral oil, for frying; 1 tablespoon fermented soybean paste (taucu); 2 tablespoons sugar; 6 tablespoons ketchup; 1 teaspoon kosher salt; 1 large egg, beaten; Chopped scallions and chiles, for garnish; Steamed Chinese buns, for serving