Put pork ribs in a pot and pour water to cover. Bring it to boil and cook for 3-4 minutes over high heat. Drain and rinse under hot water. Put them in a colander and set aside.
Heat 2 tablespoons of oil in a wok or a large skillet. Sprinkle sugar and let it caramelize over med-high heat as you stir. When the sugar turns red, add the pork ribs quickly and stir to coat. Keep stirring for 3-4 minutes.
Add the soy sauce, vinegar, chicken stock, chilies, ginger and green onion. Cover with a lid and bring it to a gentle boil, then reduce the heat to low and simmer for 20-25 minutes.
Uncover the wok and remove the ginger and the green onion. Raise the heat to high and thicken the sauce as you stir occasionally.
When the sauce starts to thicken and turns into a glaze, reduce the heat a little so that you don't burn the sauce. Continue until it becomes a very thick glaze to coat the ribs. Remove from the heat and garnish with toasted sesame oil and chopped green onion, if you wish.