- 8 slices Jewish-style rye bread, divided
- Dijon mustard
- 1 pound thinly sliced corned beef reserved from Homemade Irish Corned Beef and Vegetables
- 8 ounces thinly sliced Fontina cheese
- 1/2 sweet onion (such as Maui or Vidalia), thinly sliced
- 4 tablespoons (1/2 stick) butter, divided
- Place 4 bread slices on work surface. Spread mustard on 1 side of each. Divide corned beef among bread slices. Top with cheese and onion. Cover with remaining 4 bread slices, pressing slightly to adhere.
- Melt 2 tablespoons butter in each of 2 large nonstick skillets over medium heat. Place 2 sandwiches in each skillet and cook until golden brown on bottom, pressing occasionally with spatula, about 3 minutes. Turn sandwiches over and cook until golden on bottom and cheese melts, about 3 minutes. Transfer sandwiches to plates, cut in half, and serve.