Divide spread between 2 bread slices. Top with banana slices and remaining bread. Butter sandwich tops. Sprinkle each with 1 tsp. sugar and press to adhere. Cook sammies sugar side down in large nonstick skillet over medium-low for 2 minutes. Lightly spread butter on untoasted sides of bread; sprinkle each with another 1 tsp. sugar. Flip and cook, 2 more minutes. Quarter sandwiches; serve warm.