Spread mustard over four slices of bread. Layer with cheese, corned beef and sauerkraut. In a small bowl, mix mayonnaise, ketchup, relish and horseradish; spread over remaining bread. Place over sauerkraut. Spread outsides of sandwiches with butter.
In a large skillet, toast sandwiches over medium heat 3-4 minutes on each side or until golden brown and cheese is melted.
Notes
Toasted Reubens
New Yorkers say my Reubens taste like those served in the famous delis there. For a little less kick, you can leave out the horseradish. —Patricia Kile, Elizabethtown, Pennsylvania