Marinate the Beef: Slice the beef against the grain into thin, bite-sized pieces (about 1/4 inch thick). In a bowl, mix in the baking soda if using and let sit for 15 minutes. Rinse, pat dry, and then add soy sauce, dark soy sauce, oyster sauce, cornstarch, and water. Mix very well until the beef absorbs all the liquid. Add oil at the end to seal in the moisture. Let the beef marinate in the fridge for at least 15–20 minutes.
Prep the Egg: Crack the eggs into a bowl. Add the cornstarch slurry and salt, then beat thoroughly until you see small bubbles and the egg is evenly mixed. This step is key to getting that fluffy texture that absorbs the sauce later.
Cook the Egg: Heat about 2 tablespoons of oil in a nonstick pan over medium heat. Once the oil reaches around 220°F, pour in the egg. It should gently bubble without setting too quickly. Stir softly until just set. Avoid overcooking—runny eggs will make the sauce cloudy later. Remove and set aside.
Sear the Beef: Wipe the pan clean. Add a generous amount of oil and sear the beef over medium-high heat, about 1 minute per side, just until the slices change color. Do not overcook. Remove and drain any excess oil.
Make the Tomato Sauce: Using the remaining oil in the pan (add more if needed), sauté the chopped tomatoes. Add ketchup, soy sauce, salt, and water. Let everything simmer until the tomatoes soften and start to break down.
Combine Everything: Add the cooked egg and beef back into the pan. Stir quickly to combine and coat everything evenly in the sauce. Once everything is heated through, turn off the heat.