Combine the salt, garlic powder, pepper, paprika, and poultry seasoning in a small bowl. Rub about half of the seasoning into each pork chop. (Reserve the remaining seasoning for the gravy.) Spread 1/4 cup of the flour in a shallow dish. Dredge each pork chop in the flour.
Heat oil in a heavy skillet over medium-high heat. Add pork chops and cook until they are well browned, about 3 minutes per side. Transfer the pork chops to a paper towel-lined plate to drain.
Add the onion to the skillet (don't pour off any drippings). Cook until the onion is softened and beginning to brown, about 7-8 minutes. Add the remaining 1/4 cup flour and cook, whisking constantly until the mixture is thickened and golden brown. Add the chicken broth and whisk until smooth. Stir in the remaining seasoning. Bring the mixture to a boil over medium-high heat. Return the pork chops to the skillet and add the rosemary. Reduce heat to a simmer, cover, and cook until the pork is tender, about 1 hour.