1: Place 4 slices of bread on work surface. Spread each slice with ¼ of dressing and of mustard. Top each with ¼ of corned beef, 2 pickle slices and 1 slice of cheese. Top with remaining bread slices.
2: Butter one side of each sandwich with half of butter. Place, butter side down, in skillet set over medium-low heat. Cook for about 5 minutes or until crisped and browned. Butter top slice of bread; flip and cook for 3 to 5 minutes or until crisped and cheese is melted. Serve warm.