In a small saucepan, whisk together the cornstarch and cold water until smooth and no lumps. Then, whisk in the sugar, soy sauce, vinegar, garlic, and ground black pepper.
Bring to a boil over medium heat then reduce it and simmer until thickens.
To freeze it, wait until room temperature (or cooled in frig), then place in storage container in smaller portions. I do 1-cup portions as most of the recipes I make take 1/2 cup. When I take out a portion, I'll usually make 2 recipes that week with it. We love it!