The long, red chillies are generally mild, but not always, so as a precautionary measure when chopping them you may choose to wear disposable gloves.
In a small saucepan place the sugar, 1 cup water, rice wine vinegar, garlic and chillies. Bring to a boil, stirring to disolve the sugar and simmer rapidly on medium to high heat for 12 minutes.
Mix the cornflour with the cold water. Lower the heat, and re-stir the cornflour and water mixture as the cornflour tends to settle if made a little in advance.
Add the cornflour and water to the chillies, stir well and simmer for about 3 minutes.
Allow the mixture to cool for a few minutes. This helps to evenly distribute the chillies through the mixture.
Decant into a sterilised* jar or bottle.