Pat pork chops dry with a paper towel. Season liberally with salt and pepper on all sides.
Heat butter and oil in a large skillet over medium heat. Brown pork chops on both sides (about 2-3 minutes per side). Remove pork chops from the skillet; drain fat off the pan, but leave browned bits in the bottom (you don’t need to wipe it clean).
Add water, celery, onion soup mix, and garlic powder; stir to combine, scraping up the browned bits from the bottom of the pan to add flavor to the sauce. Return pork chops to the skillet; cover, and cook over low heat for about 15-20 minutes (or until the pork chops reach an internal temperature of 145 degrees F). Remove chops from the skillet and set aside on a plate.
In a separate bowl, toss mushrooms with flour.
Add mushrooms and flour, parsley, and milk to the skillet. Whisk and cook over low heat, just until sauce thickens (about 2 minutes). Return pork chops to the skillet and heat just until warmed through. Spoon sauce over chops and serve with cooked rice. Garnish with fresh parsley, if desired.