In a mixing bowl, combine ground beef, breadcrumbs, egg, garlic powder, onion powder, salt, and pepper.
Roll into 1-inch meatballs and place on a plate.
Brown the meatballs in a skillet for 2-3 minutes per side (optional but adds flavor).
Place the meatballs in the slow cooker.
Sprinkle the ranch seasoning and au jus gravy mix over the top.
Add the sliced butter evenly over the meatballs.
Place the pepperoncini peppers on top and pour in pepperoncini juice.
Cover and cook on LOW for 4-6 hours or HIGH for 2-3 hours.
Stir gently before serving to coat the meatballs in the sauce.
Serve hot over mashed potatoes, rice, or noodles.
Garnish with extra pepperoncini slices if desired.