Beat the egg in a medium sized bowl. Add the sliced beef, vegetable oil, and salt. Mix well and let marinate for 15 to 20 minutes while preparing the other ingredients.

Combine everything for the sauce in a big bowl and mix well.

When you’re ready to cook, drain the extra liquid from the bowl of beef. Add the cornstarch. Stir to coat the beef, until it forms an uneven coating with a little dry cornstarch left unattached.

Heat oil in a large nonstick skillet (or a cast iron pan) over medium high heat until hot. Add the beef and spread into a single layer in the skillet. Separate the beef pieces with a pair of tongs or chopsticks.

Cook without touching the beef for 2 to 3 minutes, or until the bottom turns golden. Flip to brown the other side, 1 to 2 minutes. Transfer the beef to a big plate and remove the pan from the stove. Let cool for 2 to 3 minutes.

Place the pan back onto the stove and turn to medium heat. You should still have 1 to 2 tablespoons of oil in the pan. If not, add more.

Add the onion, pepper, and dried chili pepper. Cook and stir for 1 minute.

Add the ginger and garlic. Stir a few times to release the fragrance.

Stir the sauce again to dissolve the cornstarch completely. Pour into the pan. Stir and cook until it thickens a bit.

Add back the beef pieces. Stir to coat beef with sauce.

Transfer everything to a plate immediately and garnish with roasted sesame seeds, if using.

Serve hot over steamed rice as a main dish.