Butter each slice of bread generously, making sure to cover all edges.
Assemble the Sandwich:
Layer cheddar, brie, and mozzarella on one slice of bread.
Add caramelized onions or drizzle honey if using.
Top with the second slice of bread, buttered side up.
Cook the Sandwich:
Heat a skillet over medium heat.
Place the sandwich in the skillet and grill for 3–4 minutes per side, pressing gently for even browning.
Cook until the bread is golden and crispy, and the cheese is fully melted.
Serve:
Slice and serve immediately with tomato soup or a tangy pickle for a perfect pairing.
