Toss the cauliflower with the corn flour, salt and pepper. Heat the oil in a deep wok / pan and fry the cauliflower in a couple of batches, till crispy. Drain and keep aside. Fry the already fried cauliflower another time and drain again on paper towels.
In another deep pan or a wok, heat the grapeseed oil and add the garlic to it. Once the garlic starts browning a little, add the ginger, red chillies, brown sugar, shaohsing wine, soy sauce, rice wine vinegar and ketchup. Whisk away till they all mix well together and the sugar melts. It should become a sticky, glazed sauce. Check for salt and add more if needed.
Toss the fried cauliflower in this while on low heat. Switch off heat, garnish with scallions and serve immediately.