1 1⁄2 Pound, thinly sliced (From The Delicatessen)
Split onion rolls.
Place a 1/2-inch layer of corned beef on bottom half of bun.
Spread mustard on top half and place on corned beef.
Wrap securely in squares of aluminum foil and heat in a 350Â° F oven, 12 to 15 minutes.