Pork Stew with Hard Cider and Parsnips

¼ pound pancetta or slab bacon, diced
1 ½ pounds pork butt, fat trimmed and cut into 2-inch pieces
Sea salt
1 large sweet onion, diced
1 pound parsnips, peeled and diced
2 teaspoons finely chopped rosemary
1/3 cup bourbon or calvados (apple brandy)
One 12-ounce bottle hard cider
1 tablespoon apple cider vinegar
2 cups chicken stock
1 tablespoon room temperature butter
1 tablespoon flour (I used GF AP flour)
1 tablespoon Dijon mustard