Ingredients
Instructions
- Combine cheeses, mayonnaise, mustard, and chopped onion.
- Spread mixture on one side of 4 of the bread slices to within 1/4-inch of edges.
- Top with remaining bread slices.
- Spread softened butter on the outer sides of the sandwiches.
- Cook over medium heat in a hot skillet or griddle until golden brown, turning once.