Lightly butter one side of each bread slice. Place one cheese slice on the buttered side of each of four bread slices. Top with a slice of ham, and another slice of cheese. Close the sandwiches with the remaining bread slices, buttered side in. Melt two tablespoons butter in large, heavy skillet over medium-low heat. Add the sandwiches, in batches, and cook until golden brown, adding more butter as necessary, about two minutes per side. Serve immediately.