Put 2 tablespoons of oil in the pan, then fry the finely chopped spring onion, garlic, and ginger on a low fire.
When the garlic and ginger start to become fragrant, add the bean sauce and stir-fry further
When the bean sauce has dissolved in the oil, add the ketchup and sake. Fry the ketchup for a more authentic taste.
When the ketchup has dissolved in the oil, add the chicken broth, soy sauce, sugar and pepper, and bring to a boil.
When the sauce comes to a boil add the potato starch which has been dissolved in some extra water, thickening the sauce.