Slow Cooker Pork Sirloin Roast with Mushroom Garlic Butter

This slow cooker pork sirloin roast is the definition of set-it-and-forget-it. With just four ingredients — a pork roast, onion soup mix, cremini mushrooms, and garlic-herb butter — you can create a deeply savory, melt-in-your-mouth dinner that tastes like you simmered it all day on the stove.

The magic happens as the butter melts into the meat, creating a rich, aromatic gravy that coats every shred of pork and every mushroom. Serve it over buttered egg noodles and you have a comforting, hearty meal that will become a weeknight favorite.

Slow cooker recipes are beloved for their simplicity, and this one takes that to the next level. You literally place the pork in the slow cooker, sprinkle over the onion soup mix, scatter mushrooms around the sides, and top with pats of garlic-herb butter. Then you cover it, walk away, and let the slow cooker do all the work.

Hours later, you return to a pot of fork-tender pork swimming in a savory, buttery sauce. It's the perfect dinner for busy days when you want a home-cooked meal without the fuss. The pork sirloin roast is a lean cut that becomes incredibly tender when cooked low and slow, and the mushrooms soak up all the delicious flavors.

Ingredients

Why this recipe works

Cooking a pork sirloin roast low and slow in a slow cooker breaks down the connective tissue, turning a lean, sometimes tough cut into succulent, shreddable meat. The gentle, moist heat of the slow cooker allows the collagen to melt into gelatin, which gives the pork its melt-in-your-mouth texture. Unlike a dry oven roast, the slow cooker keeps the meat bathed in its own juices, ensuring it never dries out.

The combination of dry onion soup mix and garlic-herb butter creates a deeply savory, aromatic sauce with minimal effort. The soup mix provides a concentrated umami base with onion and herbs, while the butter adds richness and a silky mouthfeel. As the butter melts, it carries the flavors throughout the pot, coating the pork and mushrooms in a luxurious gravy that makes every bite irresistible.

Notes and substitutions

The key to this recipe is using a boneless pork sirloin roast. It's a relatively lean cut, so slow cooking is essential to keep it moist and tender. If you prefer a richer, fattier result, you can substitute a pork shoulder or butt, but you may need to increase the cooking time slightly.

The dry onion soup mix is a pantry staple that adds a ton of flavor for almost no effort. If you don't have it, you can use a packet of French onion soup mix or a combination of onion powder, garlic powder, and dried herbs.

The garlic-herb compound butter, often called cowboy butter, is what makes this dish special. It's a blend of butter, garlic, and herbs like parsley, thyme, and rosemary. You can buy it pre-made or make your own by mixing softened butter with minced garlic, chopped fresh herbs, and a pinch of salt and pepper.

The butter melts into the sauce, infusing everything with a rich, savory flavor. For the mushrooms, cremini (baby bella) mushrooms are ideal because they hold their shape and have a deeper flavor than white button mushrooms.

• boneless pork sirloin roast: boneless pork shoulder or pork butt (will be even more tender, but may need extra time)
• dry onion soup mix: 1 packet of dry French onion soup mix (use same amount)
• cremini mushrooms: white button mushrooms or baby bellas (just halve them)
• garlic-herb compound butter: 4 tablespoons salted butter mixed with 2 minced garlic cloves and 1 teaspoon dried herbs (thyme, rosemary, or oregano)

Equipment

• Slow cooker (6-quart or larger)
• Measuring spoons
• Cutting board
• Chef's knife
• Serving spoon
• Large fork for shredding