Season beef roast with salt and pepper. Melt 1 Tbsp. unsalted butter in a skillet over medium-high heat, then add the beef. Allow it to sear for 4 minutes on each side to give it a caramelized coating. Once seared, add the beef tips to your slow cooker. Top with sliced yellow onion, peeled whole garlic cloves, and thyme.
1½ pounds Beef round Roast cut into chunks, ½ teaspoon black pepper, 1 tablespoon unsalted butter, 1 yellow onion, 5-6 cloves garlic, 1 sprig fresh thyme, 1 teaspoon kosher salt
Reduce the heat of the skillet to medium and melt ½ tablespoon unsalted butter. Add sliced mushrooms with a pinch of salt and stir to coat with the butter. Saute for 5 minutes, until the mushrooms are soft. Stir occasionally, scraping up the brown bits from the bottom of the pan. Add water and beef base to the skillet and stir to combine. Then, add the contents of the skillet to the slow cooker with your beef tips.
½ tablespoon unsalted butter, 8 ounces white mushrooms, 1 pinch salt, 1½ cups water, ½ tablespoon beef base
Cover your crockpot and cook on low for 5 hours, or on high for 2½ hours, until the beef is fork-tender. If you have more time, you can cook for 6 hours for even greater flavor.
Once the beef tips are done cooking, combine red wine with cornstarch and add it to the slow cooker. Turn heat up to high and cook for 20 minutes to thicken the gravy. Alternatively, cook gravy in a pan (see note 3).
½ cup red wine, 1 tablespoon cornstarch