Cowboy Butter Portobello Sirloin Tips: Easy Crockpot Dinner

This is the set-it-and-forget-it dinner that delivers big flavor with almost no effort. Tender sirloin tips, meaty portobello mushrooms, and sweet shallots simmer all day in a rich garlic-herb butter and au jus gravy. Just dump everything into the slow cooker, walk away, and come back to a meal that tastes like it took hours of hands-on work. Serve it over creamy mashed potatoes for the ultimate comfort food.

This recipe turns a handful of humble ingredients into a deeply savory, fork-tender dinner that feels special enough for a weekend but easy enough for a busy weeknight. The slow cooker does all the work: the beef breaks down into buttery-soft bites, the mushrooms soak up the rich gravy, and the shallots turn sweet and jammy.

The garlic-herb butter melts into the au jus, creating a luscious sauce that coats every spoonful. Serve it over mashed potatoes, egg noodles, or crusty bread to soak up every last drop.

Ingredients

Why this recipe works

The slow cooker is the secret here. Low, gentle heat breaks down the collagen in the sirloin tips, turning a relatively lean cut into fork-tender morsels that practically fall apart.

Unlike a quick sear, which can leave steak chewy, the long, moist heat of the Crockpot allows the meat to relax and become incredibly succulent. The mushrooms and shallots also benefit: they soften and release their natural juices, mingling with the butter and au jus to create a deeply flavorful gravy.

The combination of garlic-herb butter and dry au jus mix is a shortcut that punches far above its weight. The butter adds richness and a silky mouthfeel, while the au jus mix provides savory umami and a hint of salt.

Because everything cooks together in one pot, the flavors meld and concentrate without any extra steps. There's no searing, no deglazing, no stirring—just layer the ingredients and let time work its magic.

Notes and substitutions

Top sirloin steak tips are the ideal cut here because they have enough marbling to stay moist during the long cook, but they're leaner than chuck or brisket. If you can't find pre-cut tips, buy a whole sirloin steak and cut it into 2-inch pieces. Portobello mushrooms add a meaty texture that complements the beef, and shallots bring a mild onion sweetness that doesn't overpower the dish.

Garlic-herb cowboy butter is a flavored butter usually made with garlic, parsley, thyme, and sometimes a touch of chili flakes. It's sold in many grocery stores, but you can also make your own by mixing softened butter with minced garlic and dried herbs.

The dry au jus mix is a pantry staple; look for it near the gravy mixes. If you prefer a thicker gravy, you can whisk in a cornstarch slurry at the end, but the video keeps it simple.

• top sirloin steak tips: chuck roast cut into 1-inch cubes (cook just as tender, but trim excess fat first)
• portobello mushrooms: cremini mushrooms, halved (they hold up well in the slow cooker and are easier to find)
• shallots: 1 small yellow onion, cut into wedges (sweeter and milder, but still meltingly soft)
• garlic-herb cowboy butter: 4 tablespoons unsalted butter plus 2 minced garlic cloves and 1 teaspoon dried thyme

Equipment

• 6-quart slow cooker
• Large spoon
• Cutting board
• Chef's knife
• Measuring cups and spoons
• Serving plates