Cornstarch Needs to Be Slurried, Not Dumped In
Cornstarch thickens by having its starch granules swell and burst open when heated in liquid, releasing molecules that trap water and thicken the mixture — but added dry directly to a hot liquid, the outside of each granule gelatinizes almost instantly and forms a barrier that keeps water from ever reaching the center, leaving hard little lumps. Mixing cornstarch with a small amount of cold liquid first (a slurry) separates the granules so they hydrate evenly once stirred into the hot dish.
Sources & methodology: These tips draw on established food-science references —
Harold McGee's food-science writing, America's Test Kitchen /
Cook's Illustrated testing, Serious Eats'
technique reporting, USDA food safety guidance,
and peer-reviewed food-safety research (including UC Davis
cutting-board studies) — not reworded recipe-blog consensus.