You can either use corned beef brisket that you have cooked yourself, or the stuff out of a can. Also, some people use Thousand Island dressing instead of the Reuben dressing, but I find it too sweet for my taste.
Sliced corned beef brisket
Sauerkraut, rinsed and drained
Swiss cheese slices (one per sandwich)
Butter or margarine
Reuben dressing made from--
1/4 cup mayonnaise
1/4 cup catsup
2 teaspoons horseradish
2 tablespoons ballpark-type mustard
1 tablespoon minced parsley
Mix the Reuben dressing ingredients together (should make enough for 6 to 8 sandwiches). Or, substitute Thousand Island dressing.
Spread one side of rye bread lightly with butter. Place butter-side down in a large skillet. Spread the facing side with Reuben dressing. Layer corned beef, sauerkraut and Swiss cheese onto the bread. Spread another slice of rye bread with Reuben dressing, top each sandwich, and spread the outer side with butter. Grill each side over medium heat until cheese melts and bread is toasted.