Brush the slices of bread with melted butter in both sides.

Place the brushed bread in a baking sheet and toast in a 400 °F preheated oven. Flip the slices half way through.

To assemble the Croque monsieur, brush 2 slices of the toasted bread with mustard.

 Add a third amount of gruyere and parmesan on top for each slice of bread.

Top with few slices of turkey.

Add a third amount of gruyere and parmesan again.

Place another slice of bread on top of each loaded slice.

Top with a generous amount of bechamel sauce, spread evenly.

Finish with the rest of the two cheeses.

Place the two sandwiches under the broiler in the medium or lower rack to avoid burning the cheeses.

Once the cheeses bubble and slightly brown, take out of the oven.

 Enjoy.