Total preparation and cooking time: 50 to 55 minutes 12 ounces reserved corned beef brisket, coarsely chopped* 3 teaspoons butter, divided 1/2 cup chopped onion 2 teaspoons chopped fresh thyme 2 tablespoons reserved horseradish-butter mixture* 2 cups reserved potato halves* 1 cup shredded Swiss cheese 1/4 cup shredded Parmesan cheese l. Heat oven to 375°F Melt 2 teaspoons butter in large…