Pork Schnitzel

Name: Pork Schnitzel
Ingredients: 3 tablespoons grapeseed oil, plus more for frying; 2 medium onions, sliced thin; 1 pound button mushrooms, sliced; Kosher salt and freshly ground black pepper; 2 rosemary sprigs; 1/4 cup dry white wine; 3/4 cup beef stock; 2 large eggs; 1/2 cup sour cream; 1/8 teaspoon freshly grated mace; 1/8 teaspoon freshly grated nutmeg; 2 cups panko, pulsed for a few seconds in food processor; 1/2 cup grated Parmigiano-Reggiano cheese; 1 1/2 cups all-purpose flour; Two 6-ounce boneless pork loin chops, lightly pounded to 1/4 inch thick; Flaky sea salt and finely grated lemon zest, for sprinkling; Whole-grain mustard, for serving