Dinner · Part 3 of 3: Tips & recipe card

Slow Cooker Bourbon Portobello Flank Steak Tips, FAQ & printable recipe

Name: Slow Cooker Bourbon Portobello Flank Steak
Prep time: 10 min
Cook time: 6 h
Total time: 6 h 15 min
Cuisine: American
Ingredients: 2 lb flank steak, thinly sliced against the grain; 8 oz portobello mushrooms, thickly sliced; 6 shallots, peeled; 1 1/2 cups bourbon mushroom gravy (store-bought or homemade); 4 tbsp salted butter, cut into pats

By Clara Weller · Oct 28, 2026

Slow cooker flank steak with portobello mushrooms and bourbon gravy, bubbling in a black Crockpot.

Prep: 10 min
Cook: 6 h
Total: 6 h 15 min
Serves: 6

Includes 5 min resting

Tips for success

For the most tender beef, always slice the flank steak against the grain. This shortens the muscle fibers, making the meat easier to chew.

If you’re unsure which way the grain runs, look for the lines in the meat and slice perpendicular to them. If the steak is partially frozen, it’s easier to slice thinly. A sharp knife is essential for clean cuts.

The bourbon gravy can be enhanced with a splash of extra bourbon or a teaspoon of Dijon mustard for added depth. If you prefer a thicker sauce, mix a tablespoon of cornstarch with two tablespoons of cold water and stir it into the slow cooker during the last 30 minutes of cooking.

For a richer flavor, you can also add a splash of heavy cream just before serving, though this will change the color and richness.

Variations

Mushroom and Onion: Swap the shallots for a large yellow onion, cut into wedges. Add an extra 4 oz of mushrooms for a more mushroom-forward dish. The flavor will be slightly more savory and less sweet.
Beef and Broccoli: Add 2 cups of broccoli florets during the last 30 minutes of cooking. The broccoli will steam in the gravy and add a fresh, crisp texture. Serve over rice for a complete meal.
Spicy Bourbon: Add 1-2 teaspoons of sriracha or a pinch of cayenne pepper to the gravy before pouring it over the meat. The heat will balance the sweetness of the bourbon and add a kick.
Creamy Bourbon: Stir in 1/2 cup of heavy cream during the last 15 minutes of cooking. The cream will add a velvety richness to the sauce, making it even more indulgent. Serve over mashed potatoes.

Storage and make-ahead

Fridge: Store leftovers in an airtight container in the refrigerator for up to 4 days. Reheat gently, adding a splash of broth if needed.
Freezer: Freeze in a freezer-safe container for up to 3 months. Thaw overnight in the refrigerator before reheating.
Reheat: Reheat in a saucepan over medium-low heat, stirring occasionally, until hot and bubbling. Add a splash of beef broth if the sauce is too thick.

Refrigerate leftovers in an airtight container for up to 4 days. The flavors will continue to meld, making the leftovers even more delicious. Reheat gently in the microwave or on the stovetop, adding a splash of beef broth or water if the sauce has thickened too much. The beef can also be shredded and used in sandwiches or tacos.

This dish can be assembled the night before. Layer all the ingredients in the slow cooker insert, cover, and refrigerate overnight. In the morning, place the insert in the slow cooker and cook as directed.

You may need to add 30 minutes to the cooking time since the ingredients start cold. Alternatively, cook the dish fully, then cool and refrigerate. Reheat gently before serving.

Serving ideas

Serve this bourbon portobello flank steak over steamed white rice, which soaks up the rich gravy beautifully. Mashed potatoes or buttered egg noodles are also excellent choices.

For a lighter option, serve it over cauliflower rice or with a side of roasted green beans. The dish is hearty enough to stand alone, but a simple green salad with a tangy vinaigrette can balance the richness.

Garnish with chopped fresh parsley or chives for a pop of color, if desired. The dish pairs well with a glass of bourbon or a full-bodied red wine like a Cabernet Sauvignon. For a complete meal, add a side of crusty bread to mop up the last bits of gravy. This is comfort food at its finest, perfect for a cozy weeknight dinner or a casual gathering.

Frequently asked questions

Can this recipe be made on the stovetop or in the oven?

Yes, you can make this on the stovetop or in the oven. For the stovetop, brown the beef in a Dutch oven, then add the remaining ingredients, cover, and simmer on low for 1 1/2 to 2 hours, or until tender. For the oven, brown the beef in an oven-safe pot, add the ingredients, cover, and bake at 325°F (165°C) for 2 to 2 1/2 hours.

What can be used instead of bourbon gravy?

If you don't have bourbon gravy, use 1 1/2 cups of beef broth mixed with 2 tablespoons of bourbon and 1 tablespoon of Worcestershire sauce. You can also use a mushroom gravy or a brown gravy from a packet, prepared according to the package directions. The flavor will be slightly different but still delicious.

How can the sauce be thickened?

If the sauce is too thin, mix 1 tablespoon of cornstarch with 2 tablespoons of cold water and stir it into the slow cooker during the last 30 minutes of cooking. Let it cook until the sauce thickens. Alternatively, remove the beef and mushrooms, then simmer the sauce on the stovetop over medium heat until it reduces to your desired consistency.

Can this recipe be doubled?

Yes, this recipe can be doubled, but you will need a larger slow cooker (at least 8 quarts) to accommodate the extra ingredients. The cooking time may need to be increased by 30 to 60 minutes. Make sure the slow cooker is not filled more than three-quarters full to ensure even cooking.

What is the best way to slice flank steak?

To slice flank steak thinly, place it in the freezer for about 15 minutes to firm up. Then, using a sharp knife, cut against the grain into thin strips. The grain runs lengthwise, so slice perpendicular to the lines. Slicing against the grain shortens the muscle fibers, making the meat more tender.

Recipe card

Slow Cooker Bourbon Portobello Flank Steak

Prep 10 minCook 6 hRest 5 minTotal 6 h 15 minServes 6

Ingredients

2 lb flank steak, thinly sliced against the grain
8 oz portobello mushrooms, thickly sliced
6 shallots, peeled
1 1/2 cups bourbon mushroom gravy (store-bought or homemade)
4 tbsp salted butter, cut into pats

Instructions

Place the sliced flank steak in the bottom of a 6-quart or larger slow cooker. Spread the slices evenly to cover the bottom. Layer the thickly sliced portobello mushrooms over the beef, then scatter the peeled shallots over the mushrooms. Pour the bourbon mushroom gravy over everything, making sure the sauce coats the top. Dot the surface with the butter pats.
Cover the slow cooker with the lid. Cook on LOW for 6 to 8 hours, or on HIGH for 3 to 4 hours, until the beef is fork-tender and the sauce is bubbling. Avoid lifting the lid during cooking to keep the heat inside. Let it rest for 3 minutes before slicing.
After the cooking time, check the beef for tenderness. It should shred easily with a fork. If it is still chewy, continue cooking for another 30 minutes and check again. Once tender, let the meat rest in the sauce for at least 3 minutes before serving.
Spoon hot cooked rice onto plates or into bowls. Ladle the beef, mushrooms, shallots, and gravy over the rice. Serve immediately, with extra gravy on the side if desired.

Contains: milk, gluten

Estimated nutrition per serving

Calories: 450
Protein: 38 g
Carbohydrates: 18 g
Fat: 24 g

Automatic estimate from the ingredient list, not laboratory-verified.

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This recipe is based on a short cooking video and is published under the pen name Clara Weller. It was checked before publication, but errors can slip through. Nutrition, when shown, is an estimate. Read more in our editorial policy and on our food safety page.