“Spreading a mixture of mayo and butter on the bread creates a delightfully crispy crust with the well-loved, wonderful flavour of butter one expects on a grilled cheese sandwich.” —Josh Rink, Taste of Home Food Stylist
Spread 3 tablespoons butter on 1 side of bread slices. Toast bread, butter side down, in a large skillet or electric griddle over medium-low heat until golden brown, 2-3 minutes; remove. In a small bowl, mix together mayonnaise, Manchego cheese, onion powder and remaining 3 tablespoons butter. In another bowl, combine cheddar, Monterey Jack and Gruyere.
To assemble sandwiches, top toasted side of 4 bread slices with sliced Brie. Sprinkle cheddar cheese mixture evenly over Brie. Top with remaining bread slices, toasted side facing inward. Spread mayonnaise mixture on the outsides of each sandwich. Place in same skillet and cook until bread is golden brown and cheese is melted, 5-6 minutes on each side. Serve immediately.