This slow cooker 3-ingredient butter beef sirloin is the kind of dish that quietly steals the show at Sunday dinner. It came out of necessity one busy harvest season, when I had good beef, a stick of butter, a jar of au jus concentrate, and not much else in the pantry. I tucked it all into the slow cooker before church, and by the time we sat down to eat, the meat was so tender and flavorful that my usually chatty daughter-in-law just stared at her plate, shook her head, and said nothing at all. My son laughed and said, “Dad, this is the only thing I’ve ever seen make Mom speechless at Sunday dinner.” The secret is letting good sirloin bathe all day in butter and a rich, salty beef au jus until it tastes like something from a steakhouse, even though it only took a few minutes of your hands-on time.
Serve this butter beef sirloin sliced thick with plenty of the buttery juices spooned over the top. Around here, it sits beside mashed potatoes or buttered egg noodles to soak up every drop of that sauce. A simple side of green beans, corn, or a tossed salad balances the richness. Warm dinner rolls or crusty bread are perfect for dipping into the slow cooker juices. For a more casual meal, pile the sliced beef onto toasted buns with a ladle of the hot butter-au jus mixture for a Midwestern-style hot beef sandwich.
Slow Cooker 3-Ingredient Butter Beef SirloinServings: 6
Ingredients
3 to 3 1/2 pounds beef sirloin roast (or thick-cut beef sirloin steaks, about 2 to 3 inches thick)
1 cup prepared beef au jus (made from au jus concentrate or packet, mixed according to package directions)
1 cup (2 sticks / 16 tablespoons) unsalted butter, cut into chunks
Directions
Pat the beef sirloin dry with paper towels. This helps it cook up with better color and texture as it gently braises.
Lay the beef sirloin in the bottom of a 5- to 7-quart slow cooker. If using multiple thick sirloin steaks instead of one roast, arrange them in a single layer as much as possible.
Pour the prepared beef au jus evenly over the top of the sirloin, making sure some of the liquid runs underneath the meat so the bottom stays moist as it cooks.
Scatter the chunks of butter over and around the beef sirloin. As it melts, the butter will mingle with the au jus and natural juices from the meat to create a rich, glossy sauce.
Cover the slow cooker with the lid. Cook on LOW for 7 to 9 hours, or on HIGH for 4 to 5 hours, until the sirloin is very tender when pierced with a fork but still holds together in thick slices. Cooking on LOW will give the most tender, restaurant-style texture.
Once the meat is done, carefully lift the sirloin out of the slow cooker onto a cutting board, letting any excess butter sauce drip back into the crock.
Let the beef rest for 10 minutes so the juices settle. Then slice it across the grain into thick slices, about 1/2 inch or so, for that classic Sunday roast look.
Skim off any large pools of clear butter from the surface of the cooking liquid if you like a slightly lighter sauce, or simply stir everything together for a richer finish.
Return the sliced beef to the slow cooker, nestling the slices back into the warm butter-au jus mixture. Spoon some of the sauce over the top so every piece is glistening.
Cover and keep the slow cooker on WARM until ready to serve, letting the meat soak in the buttery juices. Serve the beef straight from the slow cooker, spooning extra sauce over each portion at the table.
Variations & Tips
For a slightly deeper flavor without adding more ingredients, choose a well-marbled sirloin roast; the natural fat will enrich the sauce as it cooks. If you only have salted butter, reduce the amount of au jus or use a low-sodium version to avoid an overly salty dish. You can also use a leaner cut like top round or eye of round, but understand it may be a bit less tender than sirloin and benefits most from the LOW and slow option. If you’d like a thicker gravy-style sauce while still keeping to the spirit of the three ingredients, remove some of the butter-au jus mixture at the end, simmer it in a small saucepan, and reduce it by about one-third; then pour it back over the beef. Leftovers reheat beautifully: store cooled meat and sauce together in a covered container in the refrigerator and use within 3 to 4 days, or freeze for up to 3 months. For food safety, keep the beef refrigerated at or below 40°F (4°C), and do not leave it sitting out at room temperature for more than 2 hours (1 hour if the room is very warm). Always ensure the beef reaches a safe internal temperature of at least 145°F (63°C) with a 3-minute rest before slicing, though most slow cookers will take it beyond that into the tender pot-roast range. When reheating, bring the meat and sauce to at least 165°F (74°C) before serving.
