Make the marinade by mixing together the sugar, salt, soy sauce and cornflour slurry. Mix in the spare ribs, let marinate for 15 minutes.
Meanwhile, boil the chestnuts for 10 mins. Peel the shell off while still warm.
Heat a frying pan with half of the oil over high heat. Stir fry the potatoes until brown. Transfer the potatoes into a saucepan and cover with water. Bring to the boil and cook over medium heat for 10 minutes.
Heat the same frying pan with the remaining oil. Stir fry the garlic until aromatic, 2-3 minutes. Add the spare ribs and cook until done, about 5 minutes.
Transfer the ribs and chestnuts into the saucepan with potatoes and add enough water to cover 3/4 of the ingredients. Bring to the boil, then simmer for an additional 20 minutes over medium-high heat. Add soy sauce and salt to taste. Garnish with spring onions, if desired.