Pat the beef tips dry with paper towels. In a large bowl, toss the beef with kosher salt, black pepper, onion powder, garlic powder, and paprika until all pieces are evenly coated.
2 to 2 1/2 pounds beef stew meat or beef tips, 1 1/2 teaspoons kosher salt, 1 teaspoon black pepper, 1 teaspoon onion powder, 1 teaspoon garlic powder, 1 teaspoon paprika
Heat the olive oil in a large skillet over medium-high heat until hot and shimmering. Working in batches, add the seasoned beef in a single layer without crowding the pan. Sear for 2–3 minutes per side, until nicely browned. Transfer browned beef tips to the crock pot as you finish each batch.
2 to 2 1/2 pounds beef stew meat or beef tips, 2 tablespoons olive oil
In the same skillet, add the sliced onion and mushrooms (if using). Add a splash more oil if the pan is dry. Cook over medium heat for 4–5 minutes, scraping up browned bits from the bottom of the pan. Add the minced garlic and cook for about 30 seconds, just until fragrant. Transfer the onions and mushrooms to the crock pot on top of the beef.
1 medium yellow onion, 3 cloves garlic, 8 ounces mushrooms
In a medium bowl or large measuring cup, whisk together the beef broth, Worcestershire sauce, soy sauce, and tomato paste until the tomato paste is dissolved. Stir in the dried thyme, dried parsley, and bay leaves.
2 cups low-sodium beef broth, 2 tablespoons Worcestershire sauce, 1 tablespoon soy sauce, 1 tablespoon tomato paste, 1 teaspoon dried thyme, 1 teaspoon dried parsley, 2 bay leaves
Pour the prepared cooking liquid evenly over the beef and onions in the crock pot. The liquid should almost cover the beef; if your slow cooker is very large and the liquid looks low, add an additional 1/2–1 cup beef broth or water.
Cover the crock pot and cook on LOW for 7–8 hours (for the most tender beef) or on HIGH for 3 1/2–4 hours, until the beef is very tender and easily pierced with a fork.
About 20–30 minutes before serving, whisk the cornstarch and cold water together in a small bowl until smooth. Remove the lid from the crock pot and stir the cornstarch slurry into the cooking liquid, mixing well. Cover and cook on HIGH for another 20–30 minutes, or until the gravy has thickened to your liking.
1/4 cup cornstarch, 1/4 cup cold water
Remove and discard the bay leaves. Taste the beef tips and gravy, then adjust seasoning with additional salt and pepper if needed. If using, stir in the butter for a silky finish. Garnish with chopped fresh parsley and serve hot over mashed potatoes, rice, egg noodles, or your preferred side.
2 bay leaves, 1 tablespoon butter, fresh parsley