To a large skillet, add the ground beef, onions, and cook over medium-high heat for about 8 minutes, or until the ground beef is browned and the onions are soft and translucent. If necessary, add a tablespoon olive oil if the mixture seems dry. Stir and crumble the beef as it cooks to ensure even browning.
Transfer the beef and onion mixture to the sprayed insert of a 6-quart (or 7-quart slow cooker).
Add the ketchup, ranch mix, au jus gravy mix, pepperoncini juice, brown sugar, and stir well to combine and distribute evenly.
Evenly top with the sliced pepperoncini peppers, pats of butter, place the lid on your slow cooker and cook on HIGH for 1-2 hours, or on LOW for 3-4 hours. Stir once or twice during the cooking process. Cook time is approximate and will depend on your slow cooker and how hot (or not hot) it runs as well as ambient kitchen temperature. Cook until done, whatever that means on the clock given your slow cooker.
Optional– If during the last 30 minutes or so of cooking, the meat mixture and sauce is not as thick as you'd like, you can help it tighten up by mixing 1 tablespoon cornstarch with 1 tablespoon water (or pepperoncini juice if you want more of that flavor/heat), add that slurry to the slow cooker, stir to combine, place the lid back on, and continue slow cooking for another 20-30 minutes, or as necessary. Tip– Everything always looks wetter/more soupy while it's hot and in the slow cooker. When it cools, and as time passes, it will dry out; keep that in mind when you're letting it simmer to not allow the meat mixture to get too dry. After all, these are sloppy joes.
Serve in buns or as desired.
