In a large mixing bowl, stir together the cheese and sauerkraut. Add enough dressing to coat, and mix thoroughly.
Butter each slice of bread on one side. Spread a thick layer of the cheese mixture onto unbuttered side of half of the bread slices. Top with sliced tomato and another slice of bread.
Heat a large skillet to medium-high heat. Fry sandwiches on both sides until the outside is toasted and the cheese is melted.
