Slow Cooker Bourbon Portobello Flank Steak

This slow cooker dinner is the definition of set-it-and-forget-it. Two pounds of flank steak, a pile of meaty portobellos, sweet shallots, and a rich bourbon mushroom gravy all simmer together until the beef is fork-tender.

The result is a deeply savory, glossy sauce that coats every bite. Serve it over rice for a comforting meal that feels like it took hours of hands-on work—but really, it’s just a few minutes of layering ingredients.

This recipe turns simple ingredients into a slow-cooked dinner that tastes like it came from a cozy steakhouse. Thinly sliced flank steak gets incredibly tender as it simmers low and slow in a bourbon-spiked mushroom gravy.

Portobello mushrooms add a meaty texture, while shallots melt into sweet, mellow pockets of flavor. The hands-on time is minimal: just layer everything in the slow cooker and walk away. By dinner, the house smells amazing and a hearty, satisfying meal is ready to serve over rice or mashed potatoes.

Ingredients

Why this recipe works

The slow cooker is the perfect tool for flank steak. This lean cut benefits from long, moist heat, which breaks down its fibers and turns it meltingly tender.

Cooking it on LOW for several hours allows the collagen to soften without drying out the meat, so every bite is succulent and easy to pull apart. The low temperature also gives the bourbon gravy time to meld with the beef juices, creating a sauce that’s rich, glossy, and full of layered flavor.

Layering the ingredients in the order specified ensures even cooking and maximum flavor. The steak sits at the bottom, closest to the heat source, while the mushrooms and shallots cook gently above. The gravy is poured over the top, so it seeps down through the layers as everything simmers. The butter pats melt into the sauce, adding a silky richness that balances the bourbon’s slight sweetness and the mushrooms’ earthiness.

Notes and substitutions

Flank steak is the star here—it’s lean but becomes wonderfully tender after hours in the slow cooker. Ask the butcher to slice it thinly against the grain, or do it yourself at home. If flank steak is unavailable, skirt steak or sirloin work well.

Portobello mushrooms are ideal for their meaty texture; cremini mushrooms are a good substitute. Shallots add a delicate onion flavor; if you only have a yellow onion, cut it into wedges.

The bourbon mushroom gravy is the shortcut that makes this recipe so easy. Look for a high-quality jarred gravy, or use homemade if you have it. The gravy should be rich and savory, with a hint of bourbon. If you prefer to skip the alcohol, use a beef broth-based gravy and add a splash of Worcestershire sauce for depth. Salted butter adds richness—if using unsalted, add a pinch of salt to the pot.

• flank steak: sirloin steak, skirt steak, or beef chuck, thinly sliced
• portobello mushrooms: cremini or baby bella mushrooms, thickly sliced
• shallots: 1 small yellow onion, cut into wedges
• bourbon mushroom gravy: 1 1/2 cups beef broth mixed with 2 tbsp bourbon and 1 tbsp Worcestershire sauce

Equipment

• 6-quart or larger slow cooker
• Cutting board
• Sharp knife
• Measuring cups
• Serving spoon