I have been playing with this and thanks to some help from my brother-in-law (who is a real chef), I think I have this. I'm AMAZED at how much the cornstarch step helps here!
Modified from Delish
1/4 cup plus 1 tbsp vegetable oil, divided
2 cloves garlic, minced
1 tsp ginger
1/2 cup soy sauce
1/2 cup hoisin sauce
1/4 cup beef broth
1/2 cup brown sugar
1 tbsp sweet chili sauce
1 lb steak, sliced against the grain
1/4 cup cornstarch
1 small onion, diced
In a small saucepan over medium heat, heat 1 tbsp of vegetable oil. Add garlic and onion and cook until fragrant, 2 minutes. Add soy sauce, hoisin sauce, broth, ginger, broth, sweet chili sauce and brown sugar and stir until dissolved. Bring to a boil, then reduce heat and simmer until reduced by half, 10-12 minutes.
Meanwhile in large skillet over medium heat, heat remaining 1/4 vegetable oil. In a large bowl, toss flank steak with cornstarch until fully coated. Add steak to skillet and sear until crispy, 3-4 minutes per side. Drain fat.
Add sauce and toss until combined then simmer a few more minutes. Serve with rice.
Makes 4 servings.