Wash baby Yukon Gold potatoes thoroughly and halve the larger ones. Peel and slice carrots into thick rounds. Dice onion and finely mince garlic.

Pat beef dry and season with black pepper and paprika. Heat olive oil in a skillet over medium-high heat and sear beef for 2-3 minutes per side until browned.

Transfer seared beef to a slow cooker. Arrange potatoes and then scatter carrots, onion, garlic, and whole pepperoncini on top.

In a bowl, combine beef broth, pepperoncini juice, Worcestershire sauce, and tomato paste. Whisk in ranch seasoning mix, au jus mix, and thyme until well combined.

Pour the broth mixture over the beef and vegetables. Cut butter into pieces and add on top of the stew. Cover the slow cooker.

Cook on LOW for 7-8 hours or HIGH for 4-5 hours until beef is fork-tender and vegetables are easily pierced.

Mix cornstarch with cold water until dissolved. Pour into the hot stew, stir gently, and cook on HIGH for an additional 15-20 minutes to thicken the gravy.

Taste and adjust seasoning if necessary. Switch to WARM setting and let rest for 5 minutes. Garnish with parsley before serving hot from the slow cooker.