Preheat the oven to 275°F.

Set a large Dutch oven or oven-safe pot over medium-high heat and add the butter.

Pat the beef dry with paper towels, then place it on a large plate and coat on all sides with the au jus mix and ranch seasoning. Reserve any excess seasoning that does not stick to the beef on the plate.

Once the butter is sizzling, reduce heat to medium and add the beef to the pot. Sear, without moving, until browned, 2 minutes. Flip the beef and sear an additional 2 minutes on the opposite side.

Remove the seared roast from the pan and transfer to a large plate. Slowly pour the beef broth into the pan and deglaze. Add the pepperoncini juice and stir to combine. Stir in any au jus and ranch seasoning mix leftover on the plate, as well as the second packet of ranch seasoning. Add the whole pepperoncini, and return the roast to the pan.

Remove the pot from the heat and cover.

Roast on middle rack of oven until the meat is extremely tender and easily shredded with a fork, 3 1/2-4 hours.

Check to see that pot roast is done. Remove from oven or add time as needed.

Transfer the pot roast to a large serving dish. Shred the meat with two forks. Remove the pepperoncini with a slotted spoon, and use a fork to remove the stems. Arrange over the pot roast, and serve immediately.