Go Back

Slow Cooker Mongolian Beef - Tender, Saucy, and Simple

Print Recipe Pin Recipe
Prep Time 15 minutes
Cook Time 4 hours
Total Time 4 hours 15 minutes
Servings: 6 servings
Ingredients Method

Ingredients
  

  • 2 pounds flank steak (or sirloin), thinly sliced against the grain
  • 1/4 cup cornstarch (for coating the beef)
  • 3/4 cup low-sodium soy sauce
  • 1/2 cup brown sugar (light or dark)
  • 1/2 cup beef broth (or water)
  • 4 cloves garlic, minced
  • 1 tablespoon fresh ginger, grated (or 1 teaspoon ground ginger in a pinch)
  • 1–2 tablespoons rice vinegar (to balance the sweetness)
  • 1–2 teaspoons sesame oil (for aroma)
  • 1/2–1 teaspoon red pepper flakes (optional, for heat)
  • 2–3 green onions, sliced (plus more for garnish)
  • 1 tablespoon cornstarch + 1 tablespoon water (optional slurry to thicken, if needed)
  • 2 tablespoons neutral oil (optional, for a quick sear)
  • Sesame seeds, for garnish (optional)
  • Cooked rice or noodles, for serving
  • Optional veggies: broccoli florets, snap peas, or bell peppers

Method
 

  1. Slice the beef: Cut the flank steak into thin strips against the grain. This keeps the meat tender. Pat dry with paper towels to remove excess moisture.
  2. Coat with cornstarch: Toss the beef with 1/4 cup cornstarch until evenly coated. Shake off any extra. The coating helps thicken the sauce later and creates a silky texture.
  3. Optional sear: Heat oil in a skillet over medium-high. Sear the beef in batches for 30–45 seconds per side. You’re not cooking it through—just getting a little color. This step adds flavor, but you can skip it if you’re short on time.
  4. Make the sauce: In a bowl, whisk soy sauce, brown sugar, beef broth, garlic, ginger, rice vinegar, sesame oil, and red pepper flakes. Taste and adjust. It should be savory-sweet with a gentle tang.
  5. Load the slow cooker: Add the beef to the slow cooker. Pour the sauce over the top and toss lightly. Cover with the lid.
  6. Cook low and slow: Cook on LOW for 3.5–4.5 hours or HIGH for 2–2.5 hours. The beef should be tender but not shredded like pot roast.
  7. Add green onions (and veggies): During the last 20–30 minutes, stir in sliced green onions. If adding veggies like broccoli or snap peas, add them now so they stay crisp-tender.
  8. Thicken if needed: If the sauce is too thin, stir in a cornstarch slurry (1 tablespoon cornstarch mixed with 1 tablespoon water). Cook 10–15 more minutes until glossy and thick.
  9. Finish and serve: Taste and adjust seasoning—add a splash more vinegar for brightness or a pinch of sugar if you want sweeter. Serve over rice or noodles. Garnish with extra green onions and sesame seeds.