Make a smooth cornstarch slurry for sauce
Mix the starch in cool liquid first, then judge the sauce after heating a small addition.
Cornstarch sprinkled straight into a hot sauce can form small lumps with dry centers. Before it meets the pan, stir one teaspoon of cornstarch with two teaspoons of cold water in a small cup. Press the spoon against the sides to break up any pockets. This makes a small working quantity, not a fixed dose for every sauce.
If you set the cup aside while the sauce cooks, the starch may sink and leave clear water above it. Scrape the bottom and stir it back to a smooth suspension immediately before pouring. Stir the simmering sauce as you drizzle in part of the slurry. Let the sauce return to a gentle simmer and observe the change before adding more.
Dip a spoon into the sauce and see how it coats the back. A light coating might be enough for a stir-fry, while a filling may call for a different texture and its own tested proportions. Stop adding slurry when the recipe's texture is reached. If it gets thicker than intended, stir in a small splash of the original liquid and check again.
