Chinese Take-Out's Mongolian Beef

I am a red meat kind of girl, so when I get to have beef rather than chicken for Chinese food, I am all in :).  Aaron prefers chicken most of the time, but I love me some steak/beef/what ever.  This Mongolian beef has such great flavor, and we all gave it a 9, except Aaron who gave it an 8.  Like all the recipes in Chinese Take-Out cookbook, this is relatively low in calories, but we always wish we had more sauce.  Each of the five servings was 256 calories, not including the rice, but it would be more if we made more sauce, which I plan on doing next time.  In fact, I will just post the doubled sauce recipe here, so I won't even try to make it the other way :).  Here's what to do:

Marinade:
1 T soy sauce
1 T mirin
2 t cornstarch

1 lb flank steak, sliced thinly against the grain

Sauce:
1/4 c soy sauce
4 t hoisin sauce
4 t chili paste
4 t mirin
2 t oyster sauce
2 t sesame oil
1/2 t crushed red pepper flakes

1 T oil
2 leeks, white part only sliced thinly
1 t minced fresh ginger
1 scallion, chopped

Marinate the beef in the marinade for about 10 minutes.
Mix the sauce ingredients together, then set aside.
Heat the oil in your pan, then add in the beef to stir fry for a few minutes.  Add the leeks, and ginger and stir fry for another few minutes.  Add the sauce, and stir, cooking until the beef is cooked to desired doneness.  Garnish with scallions and serve.