1Heat nonstick griddle or large skillet over medium heat. Brush 1 side of each tortilla with melted butter; place tortillas, buttered side down, on griddle.
2Top each tortilla with 1 cheese slice, 1/4 cup corned beef, 2 tablespoons sauerkraut and another cheese slice. Fold tortilla in half over filling. Cook 3 to 5 minutes, turning once, until golden brown and cheese is melted.
3Cut each quesadilla into 4 wedges. Serve with Thousand Island dressing.