In a medium bowl, toss the shrimp with just 1 teaspoon of cornstarch, salt, pepper and sesame oil. Set aside to marinate.
In the wok (or saute pan), boil 1 cups of water over medium-high heat. When water is boiling, add the broccoli florets, cover with lid and let steam/blanch for 1 minute, shaking the pan halfway through. The broccoli should be bright green, and still a little crisp. Drain and set aside. Wipe pan dry.
In a small bowl, mix the remaining 1 teaspoon cornstarch, soy sauce and oyster sauce. Set aside.
In the pan, and heat just 1 tablespoon of cooking oil over medium-high heat. Add the shrimp and stir-fry for 2 minutes, or until they turn pink. Remove from the pan and set aside.
Wipe the wok or pan clean with paper towel, then heat the remaining 1 tablespoon oil over high heat. Add the onion and snow peas and stir-fry until fragrant, about 1 minute. Add in the garlic and stir fry for an additional 30 seconds.
Pour in the chicken stock and heat to boiling, then stir in the cornstarch/soy/oyster sauce mixture and cook until the sauce thickens, about 30 seconds.
Add the baby corn and stir-fry for 1 minute. Stir in the reserved shrimp and broccoli and cook, stirring constantly for 1 minute, until the shrimp are hot.