Season the pork chops with the salt and pepper and coat them in 1/2 cup of the flour, shaking off the excess.
Heat the oil in a deep skillet over medium-high heat and brown the chops in 2 batches for 3 minutes per side, then move them to a plate.
Lower the heat to medium, add the onions, and cook for 10 minutes until soft and golden at the edges.
Sprinkle in the remaining 1/4 cup flour and thyme and stir for 1 minute, then whisk in the broth and milk until smooth.
Return the chops and their juices, cover, and simmer gently for 25 to 30 minutes until the pork reaches 145°F and the gravy coats the onions.
Rest the chops in the gravy for 3 minutes before serving.