In large pot, whisk together cornstarch and stock. Bring that mixture to a heavy simmer.
As stock heats, scramble eggs and soy sauce together. Once stock is simmering, swirl the stock in the pan (think making a whirlpool in the pot like you did in the pool as kids). Quickly pour the eggs into the edge of the whirlpool.
Cook soup for another 1-2 minutes. Serve immediately, garnished with green onions as you please.