1. Start by slicing your flank steak very thin—this helps it cook quickly and stay tender. Toss the beef slices with cornstarch in a large bowl, making sure every piece is coated. This step gives the beef a nice crust when seared.
2. Heat the vegetable oil in a large skillet or wok over medium-high heat. Once hot, add the beef slices in a single layer (you might need to do this in batches). Cook for about 2 minutes on each side until browned but not fully cooked through. Remove the beef and set aside.
3. Lower the heat to medium and add minced garlic and ginger to the same pan. Stir quickly for about 30 seconds until fragrant—this step is crucial for building flavor, so don’t rush it!
4. Pour in the soy sauce, water, and brown sugar. Stir until the sugar dissolves and the sauce starts to thicken, about 3-4 minutes. This is where your kitchen will start smelling like the best kind of comfort food.
5. Add the cooked beef back into the pan along with the white parts of the green onions and red pepper flakes if using. Toss everything together and cook for another 2 minutes, letting the sauce cling to the beef perfectly.
6. Remove from heat and sprinkle the green parts of the green onions on top for a fresh pop of color and flavor. Serve immediately over steamed rice or your favorite veggies.

From my experience, don’t overcook the beef in step 2—it’ll continue cooking in the sauce and stay tender. Also, feel free to adjust the sugar and soy sauce balance based on how sweet or salty your family likes it. My kids like it a little sweeter, so I often add a pinch more brown sugar.