Step 1

Bring a medium pot of salted water to boil, add the onions, and cook until tender but not mushy (about 12 minutes). Drain, reserving 2 cups of the cooking liquid (strained, if necessary). Rinse onions with cold water until cool enough to handle. Peel and set aside.

Step 2

Season both sides of each chop with salt and pepper. Add flour to a wide, shallow bowl and dredge pork, shaking off excess flour.

Step 3

In a 4- to 5-quart straight-sided sauté pan set over medium-high heat, add butter and olive oil. When butter stops foaming, add pork, in a single layer (work in batches if necessary). Cook pork on both sides, until lightly browned and just cooked through, about 2-3 minutes per side. Remove to a plate.

Step 4

Add the onions to the skillet, and cook until golden brown, 4-5 minutes. Add the garlic and cook for 30 seconds, then pour in wine, and bring to a simmer, scraping the pan with a wooden spoon to loosen any browned bits. Once the wine is mostly reduced, add the thyme, mustard and 1 cup of the reserved onion-cooking broth (or use chicken stock). Add the grapes and the sauce simmer until liquid is reduced by almost half and grapes soften, 5-7 minutes. Add the pork back to the skillet and toss to coat in sauce (if more liquid is needed, add some of the reserved broth). Simmer until the pork is warmed through and sauce has thickened, about 4-5 minutes.

Step 5

Transfer pork, grapes and onions to a warm serving platter. Stir balsamic vinegar into sauce. Check seasoning. Spoon sauce over pork, onions and grapes, and serve.