Step 1: Heat the Skillet - Place a large skillet over medium high heat and add the cooking oil. Give the oil a minute or two to become hot before adding the roast. You are looking for an oil surface that appears loose and shimmery, but it should not be smoking heavily. Starting with a properly heated pan helps the beef brown instead of steaming, and that browned surface adds a deeper roasted flavor to the finished meal.
Step 2: Sear the Chuck Roast - Carefully place the chuck roast in the hot skillet. Let it cook without moving it for 3 to 4 minutes, then turn it and sear the second side for another 3 to 4 minutes. If the roast has thick edges that are easy to hold with sturdy tongs, you can briefly brown those too. The beef will not be cooked through at this point, and that is exactly right. You are simply creating a dark golden crust that will bring extra flavor to the slow cooker.
Step 3: Transfer the Roast - Move the seared chuck roast into the slow cooker, placing it as flat as possible. Pour any flavorful juices from the skillet over the beef. Those browned bits and drippings may not look like much, but they carry a lot of flavor. Be careful when moving the roast since it is heavy and the hot oil can splash. A wide pair of tongs and a sturdy spatula make this step easier.
Step 4: Add the Seasonings - Sprinkle the ranch seasoning mix evenly over the top of the roast, followed by the au jus gravy mix. There is no need to add a cup of water or beef broth. The roast will release plenty of its own juices as it cooks, and the butter and pepperoncini brine will add more moisture. Keeping the added liquid limited gives you a concentrated, savory sauce instead of a thin broth.
Step 5: Add the Pepperoncini - Arrange the pepperoncini peppers over and around the roast, then spoon in a small splash of their juice. I usually start with about 1 tablespoon when cooking for the whole family. You can use a little more when your crew enjoys a stronger tang. The peppers mellow as they cook, and their bright acidity helps balance the beef, butter, and seasonings.
Step 6: Top With Butter - Cut the butter into roughly one half inch pieces and arrange them across the top of the seasoned roast. Spreading the pieces out helps the butter melt over more of the surface. As it melts, it carries the ranch and au jus seasonings down around the meat and into the cooking juices. It may look like a generous amount of butter, but it is part of what gives this roast its signature richness.
Step 7: Cook Low and Slow - Cover the slow cooker and cook the roast on low for 8 to 9 hours. Try not to lift the lid during the cooking time because each peek releases heat and can slow the process. The roast is ready when a fork slides in easily and the beef begins to separate with very little pressure. A larger or thicker roast may need the full 9 hours, while a smaller roast may become tender closer to 8 hours.
Step 8: Shred the Beef - Lift the pepperoncini from the slow cooker and set them aside for a moment. Use two forks to pull the roast into large, tender pieces. You can shred it directly in the slow cooker, which keeps all the beef coated in the flavorful juices and saves you from washing another dish. Remove any large pieces of fat that did not melt during cooking.
Step 9: Finish and Serve - Return the pepperoncini to the slow cooker when your family enjoys them, or leave them on the side so everyone can choose. Gently stir the shredded beef through the cooking juices, then let it rest for a few minutes with the lid on. This gives the meat time to soak up more of the sauce. Spoon it over mashed potatoes, rice, or another favorite base, making sure every serving gets some of those rich juices.