Step 1

Prep the sauce. In a medium bowl, stir together the soy sauce, sugar, water, sesame oil, molasses, ginger, and garlic. Set aside.

Step 2

Slice the steak. Slice the steak in half lengthwise, then slice crosswise against the grain into thin strips.

Step 3

Prep the steak. In a mixing bowl, toss the sliced flank steak with the cornstarch, shake off any excess, and then set aside on a separate plate.

Step 4

Cook the steak. Heat the oil in a large skillet or wok over medium-high heat. Add the steak to the wok and cook in small batches, for about 30 to 60 seconds on each side, until browned. Remove the cooked steak to a plate, and repeat this process until all of the steak is cooked. If needed, add a splash of more oil to the wok in between batches.

Step 5

Simmer the sauce. Reduce the heat to medium, add the sauce, and let it simmer for 4 to 5 minutes, stirring occasionally, until slightly thickened.

Step 6

Finish the Mongolian beef. Add the steak back to the wok, and stir with the sauce for 1 to 2 minutes, to reduce the sauce further and fully coat the meat. Sprinkle the sliced green onions on top, and give it one final stir before serving.