Slice potatoes into half-moon shapes, dice ham and onion, and thinly slice garlic. Soak potatoes in cold water for 10 minutes to remove starch.

Prepare the seasoning by mixing soy sauce, mirin, corn syrup, sugar, pepper, and water in a bowl.

Heat vegetable oil in a pan over high heat. Drain potatoes and stir-fry until lightly coated with oil.

Add onion and garlic to the pan, then pour the seasoning mixture over the ingredients. Reduce heat to medium and simmer.

Once the potatoes are tender and the sauce has thickened, add diced ham and cook for another few minutes.