Batter: whisk together the cornstarch, flour and white pepper in a large bowl. Add the water and egg and whisk until the batter is smooth.
Beef: toss the beef strips with the batter until they are fully coated.
Fill a large Dutch oven/pot with 2 inches of the oil. Heat the oil to 350 degrees F (177 C). Working in batches, add the beef strips to the hot oil. Use a fork to stir and break them apart as they cook. Fry the beef strips for 3 to 4 minutes or until they are golden brown. Remove the beef strips with a slotted spoon or strainer and let them drain on a baking sheet lined with paper towels. Sauce: whisk together the low sodium soy sauce, water, dark soy sauce, vinegar, brown sugar and red pepper flakes in a medium bowl. Set the sauce aside.
Stir fry: heat the sesame oil in a large skillet over medium-high heat. Add the garlic and ginger and cook them for 1 minute, or until fragrant. Add the sauce to the skillet and cook it, stirring constantly, for 1 to 2 minutes, until it has slightly thickened (won’t thicken much).
Add the fried beef strips to the skillet and toss to coat them in the sauce. Cook the beef and sauce for 1 to 2 minutes, until the sauce is thick and fully coats each beef strip. Garnish beef with the sesame seeds and green onions.