01 -  Preheat your oven to 200°C (400°F). Line a baking tray with parchment paper. 
 02 -  In a small saucepan, melt 15 g butter over medium heat. Stir in flour and cook for 1 minute. Gradually whisk in the milk and bring to a simmer, stirring until thickened. Season with nutmeg, salt, and pepper. Remove from heat. 
 03 -  Lightly toast the bread slices. Spread one side of each slice with softened butter, then a thin layer of Dijon mustard. 
 04 -  On 4 slices of bread, layer the smoked duck breast, dot with pieces of fresh goat cheese, and drizzle lightly with honey. 
 05 -  Top the filling with the remaining bread slices, buttered side out. 
 06 -  Place the sandwiches on the prepared tray. Spoon béchamel sauce over each sandwich and sprinkle generously with grated Emmental or Gruyère. 
 07 -  Bake for 10–12 minutes, or until golden and bubbling. For a crispier top, broil for an extra 1–2 minutes. 
 08 -  Serve hot, optionally with a side salad.