Use your grater to grind 2 tablespoons of garlic. Then, use a grater to grind 1 tablespoon of ginger.
Heat in a medium pot tablespoon of sesame oil over medium-high. Add in garlic, ginger and let them cook until fragrant, but do not burn.
Pour in the soy sauce, sugar, brown sugar and black pepper let them cook until it’s boiling. Reduce the heat to very low and simmering for 10-15 minutes.
Meanwhile, in a small bowl, whisk together 2 tablespoons of water and 4 tablespoons corn starch. (It is hard to stir the corn starch because it’s very thick. I suggest to add 2 tablespoons first and stir them well. After that, add the other 2 tablespoons and mix them well).
Once your slurry is ready slowly add it into the sauce and keep whisking the sauce for a minute and wait until it’s boiling again. Then, simmering for 5 minutes. Whisk frequently, but also let it thicken.
Lastly, add sesame seeds (this is optional) and stir them well.