Keeps 3 days refrigerated. The sauce thickens further when cold; loosen with a splash of water. Reheat fast in a hot pan — the microwave overcooks the beef. Store rice separately.
Usually sliced with the grain rather than against it, or overcooked. Two minutes in a hot pan is enough — it finishes when returned to the sauce.
It's called velveting. The starch forms a barrier that holds moisture in the meat and helps the sauce cling — the single biggest difference between home and restaurant stir-fry.
Yes. Mix soy, sugar, garlic, ginger and a teaspoon of cornstarch in a jar, refrigerate up to a week, and shake before using — the starch settles.