Spread butter on one side of each bread slice. Place bread buttered side up on a baking sheet.
Broil bread for 1-2 minutes until lightly toasted.
Remove from oven. Spread mayonnaise on toasted side if using. Top each slice with cheese, tomato slices, and any optional toppings. Season with salt and pepper.
Return to broiler and cook for 2-3 minutes until cheese is melted and bubbly. Serve immediately.
Tips
Use a sturdy bread like sourdough to prevent sogginess.