1. Make the spicy mayo by mixing together the hot sauce and mayo in a small dish and set aside.
2. Preheat a skillet over medium heat. Spread butter on one side of your bread slices and spread the spicy mayo on the other side. Layer your sandwich with red onion, salmon, havarti cheese, and dill. Sprinkle with salt and pepper and crown your sandwich with the other slice of bread.
3. Toast your sandwich on both sides in the skillet until golden brown and the cheese is melty. Enjoy hot and fresh!