Guinness Pork Chops in Gravy

8 (1-inch thick) pork chops
Salt and freshly ground black pepper
All-purpose flour
1 tablespoon unsalted butter
2 tablespoons vegetable oil
3 large onions, thinly sliced
3 cloves garlic, minced
8 ounces Guinness stout or full-bodied dark beer (about), divided
About 8 ounces chicken stock, divided
1 tablespoon coarse grain mustard (or more)
1 tablespoon chopped fresh parsley
1 1/2 teaspoons balsamic vinegar (or more)

Season the pork with salt and pepper. Dredge them in flour and shake off excess.

Melt the butter with 1 tablespoon oil in heavy large deep skillet over medium-high heat. Add the pork in batches and brown well, about 6 minutes per side. Transfer the pork to plate and set aside.

Dredge the onions in flour; shake off excess.

Heat the remaining 1 tablespoon of oil in the same skillet over medium heat. Add the onions and garlic. Season with salt. Cover and cook for 5 minutes, stirring once. Uncover and cook for 4 more minutes, stirring occasionally.

Add 2 ounces of Guinness, 6 ounces of the stock and bring to a boil, scraping up any browned bits.

Return the pork to the skillet. Spoon some of the onions over the pork. Add enough additional Guinness and stock to bring liquid halfway up sides of pork. Cover the skillet with foil, and then the lid. Reduce the heat and simmer for 20 minutes.

Turn the pork over and cook until very tender, about 25 more minutes. Transfer the pork and onions to a platter using a slotted spoon.

Degrease the pan juices. Boil the juices until thickened slightly, about 10 minutes.

Whisk in 1 tablespoon of mustard. Add chopped parsley and 1 1/2 teaspoons of balsamic vinegar. Taste and add more mustard or vinegar if desired.

Pour the gravy over the pork. Garnish with parsley and serve.