In a small bowl sour cream and hot sauce. Stir in chicken.
Spread the outsides of the bread with butter. Place a slice of bread butter-side down in a skillet and half of the chicken mixture. Top with a sliced of mozzarella cheese. Follow it with another slide of bread, butter-side up. Cook until the cheese is melted and sandwich is golden brown, about 4 to 5 minutes per side.Serve immediately!