01 -
Place 3 pounds sirloin steak, cut into bite-sized pieces, into a large bowl and season with 2 teaspoons kosher salt and 1 teaspoon black pepper. Toss to combine.
02 -
Get a large skillet hot over medium-high heat and add 1 Tablespoon vegetable oil. Sear the steak pieces in batches until browned, ensuring they are not cooked through. Add more oil to the pan if needed.
03 -
Add the seared steak into a 6-quart slow cooker along with 1 small sweet onion and 3 cloves garlic, both thinly sliced. Gently stir together.
04 -
Pour in 1 cup unsalted beef stock. Sprinkle the 1-ounce packet of au jus gravy mix evenly over the top, then lay 4 tablespoons of unsalted butter, thinly sliced, over the top.
05 -
Cover the slow cooker and set to high for 3-4 hours or low for 6-8 hours. Stir once an hour if possible.
06 -
Serve the steak bites with mashed potatoes, egg noodles, or rice.