Slice the pork into long length or bite-size pieces, about 1 inch thick. The thinner the pork is the more tender it will get.
Blend garlic, coriander roots, and pepper in a blender or food processor until fine.
In a mixing bowl, mix the sliced pork and blended ingredients together by hand.
Add ⅓ cup of the milk, sugar, soy sauce, oyster sauce, 1 teaspoon of the vegetable oil, dark soy sauce, corn flour, pepper, and salt. Gently mix them throughly by hand.
Cover the bowl and put the mixed pork in the refrigerator and let it marinate at least 3-4 hours (better overnight).
Place the wooden skewers in water to soak for 30 minutes.
Take the marinated pork out and let it sit at room temperature for 5-10 minutes and then start to skewer them up on the wooden skewers, which have been soaked.
Heat the grill on to medium-high heat. Use the rest of the vegetable oil to brush on the grill first so the pork does not stick to the grill. Grill for 7-8 minutes on each side and cook evenly (takes about 15 minutes until pork is cooked through). Turn skewers, and baste often with the rest of the coconut milk (or whole milk) while grilling.
Serve hot with hot sticky rice.