cut or crush the ginger into small pieces.
Mix the sugar, soy sauce, ginger, 1 cup of water, and garlic in a small pot or pan over low to medium heat.
In a cup, mix ½ a cup of water with a tbsp of corn starch until homogenous.
Add ⅔ of the water and cornstarch to the pot slowly while mixing. The mix will turn brown - continue heating and mixing until it is back to black color.
Check the consistency, if it is too thin add more of the cornstarch mixed water and check again after it is back to dark.
If after using all the cornstarch mixed water, the sauce is still too thin - make another cup of cornstarch mixed water. But don't overdo it, 2 tbsp will make the mix almost jelly-like in the refrigerator.