Melt 3 tablespoons butter in a deep pan or casserole dish. Add the onions and celery. Cook on low-medium heat until the vegetables just start to soften.
Add the ground beef. Add the salt, pepper, onion powder, celery salt, and parsley. Raise the temperature to medium heat and cook until the beef is no longer pink. Stir the beef mixture with a wooden spoon.
Stir in the tomato sauce, ketchup, and chicken stock. Cook on low-medium heat until the beef mixture thickens. This should take about 30 minutes.
When ready to serve, heat a little butter in a pan on medium heat. Lay each burger or brioche bun inside-down for a few seconds, until they start to toast up a little bit.
To assemble, add a generous serving of ground beef mixture and lay it on the bottom half of the bun. Then, add a some shredded cheddar cheese on top of that. Top that off with the top half of the bun.