Ultimate Slow Cooker Mongolian Beef

The smell that fills my house when this beef is cooking is absolutely unfair to my neighbors. My teenage son actually texted me from school asking what smelled so good, which never happens. This is the kind of meal that makes people linger around the kitchen island, pretending to help but really just waiting for a taste test.

I made this for a Tuesday dinner once when my sister was going through a rough patch at work. She took three bites, closed her eyes, and said this was the closest thing to a hug you can get from food. We ended up sitting at the table for two hours just talking, which never happens on weeknights anymore.

Ingredients

• 2 pounds flank steak, thinly sliced across the grain: Slicing against the grain is absolutely crucial here—I learned this the hard way when I ignored it once and ended up with chewy strips instead of melt-in-your-mouth beef. Partially freeze the meat for 30 minutes before slicing, it makes this step so much easier.
• 3/4 cup low-sodium soy sauce: Regular soy sauce makes this dish unbearably salty after 4 hours of cooking. I use low-sodium and still never add extra salt—the flavors concentrate plenty.
• 3/4 cup brown sugar, packed: Dark brown sugar gives you this subtle molasses note that white sugar completely misses. Pack it down in your measuring cup or you will not get enough sweetness to balance the soy.
• 1/2 cup water: This seems like a boring ingredient but it prevents the sauce from becoming too concentrated as the liquid evaporates. Trust me, I tried skipping it once.
• 1/4 cup hoisin sauce: This is the secret ingredient that gives Mongolian beef that distinctive almost five-spice flavor profile. The brand does matter—find one at an Asian market if you can.
• 1 tablespoon sesame oil: Toasted sesame oil is non-negotiable here. The regular stuff tastes like nothing and you will miss that nutty finish that makes this dish sing.
• 4 cloves garlic, minced: Fresh garlic only, never jarred. The slow heat mellow it beautifully, so do not be shy about using all four cloves.
• 1 tablespoon fresh ginger, grated: I use a microplane for this because it practically dissolves into the sauce. Peel it first or you will get fibrous bits in your silky sauce.
• 1/2 teaspoon crushed red pepper flakes: Start with this amount and taste at the end. The heat mellows significantly during cooking, so you can always add more but you cannot take it back.
• 1/4 cup cornstarch: You will use this twice—once for coating the beef and once for thickening the sauce. Measure precisely because cornstarch is unforgiving.
• 1/4 cup cold water for slurry: Must be cold. Warm or hot water turns cornstarch into weird clumpy globs instead of a smooth slurry. I learned this through a very frustrating dinner service.
• 4 green onions, sliced: Slice these right before serving or they get sad and limp. Both white and green parts add different kinds of flavor.
• 1 tablespoon toasted sesame seeds: Toast them in a dry pan for 2 minutes while the beef rests. The difference between toasted and raw sesame seeds is night and day.

Instructions

Whisk together your sauce base:

In a medium bowl, combine soy sauce, brown sugar, water, hoisin sauce, sesame oil, garlic, ginger, and red pepper flakes. Whisk until the sugar completely dissolves—no gritty texture allowed.

Coat the beef like a pro:

Toss sliced beef with cornstarch in a zip-top bag until every piece is evenly dusted. Do not skip this step because it creates that gorgeous glossy coating on the meat and keeps it tender.

Set up your slow cooker:

Transfer cornstarch-coated beef to your slow cooker and pour that beautiful sauce mixture over everything. Stir gently to distribute—some pieces will clump together and that is totally normal.

Let the magic happen:

Cover and cook on low for 4 hours. Resist the urge to open the lid—every time you do, you add 15 minutes to the cooking time and lose precious moisture.

Create your slurry:

During the last 30 minutes of cooking, whisk cornstarch and cold water until completely smooth. Pour into the slow cooker and stir gently—the sauce will thicken right before your eyes.

Finish with flair:

Serve hot over steamed rice, sprinkled generously with sliced green onions and those toasted sesame seeds you so wisely prepared earlier.

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This recipe has become my go-to for new parents and anyone recovering from surgery because it reheats beautifully and freezes exceptionally well. My neighbor actually cried when I dropped off a container of this after she had her appendix out.

Making It Your Own

I have found that adding sliced bell peppers or snap peas during the last hour of cooking gives you this incredible texture contrast. The vegetables stay slightly crisp while absorbing all that gorgeous sauce. My vegetarian daughter loves swapping the beef for extra-firm tofu—just press it really well first and skip the cornstarch coating step.

The Rice Secret

Jasmine rice is my absolute favorite pairing here because its floral notes complement the ginger and garlic perfectly. Rinse your rice until the water runs clear before cooking—it removes excess starch so each grain stays separate. Or try cauliflower rice if you are watching carbs, it honestly works surprisingly well with this bold sauce.

Make-Ahead Magic

You can slice the beef and whisk the sauce the night before, then just dump everything in the slow cooker before work. The cornstarch coating might get a little gummy overnight but it melts away during cooking. I have even prepped everything on Sunday for Monday dinner with zero issues.

• Double the sauce ingredients if you love extra sauce for your rice
• Freeze leftovers in portion-sized containers for emergency weeknight dinners
• The flavor actually gets better after a day or two in the refrigerator

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This is one of those recipes that turns an ordinary Tuesday into something people talk about for weeks. Hope it brings as much comfort to your table as it has to mine.

Common Recipe Questions

→ What cut of beef works best for this dish?

Flank steak thinly sliced across the grain is ideal for tenderness and absorbing the sauce flavors evenly during slow cooking.

→ Can I add vegetables to the slow cooker?

Yes, sliced carrots or bell peppers can be added along with the beef to provide extra texture and depth.

→ How do I thicken the sauce properly?

A cornstarch slurry mixed with cold water is added during the last 30 minutes of cooking to achieve a glossy, thickened sauce.

→ Is this dish gluten-free?

To make it gluten-free, substitute tamari for soy sauce and use a gluten-free hoisin sauce alternative.

→ What are the best serving suggestions?

Serve hot over steamed jasmine or basmati rice, or try alongside steamed broccoli for a low-carb option.