Classic Croque Monsieur with Ham and Gruyère

Season the béchamel with 1/4 teaspoon salt, a pinch of ground white pepper, and a small pinch of nutmeg. Remove from heat and stir in 50g grated Gruyère cheese until melted and smooth. Cover with plastic wrap pressed directly on the surface to prevent skin formation.

Preheat oven to 220°C (425°F) with rack positioned in upper third. Line a large baking sheet with parchment paper or a silicone mat. This high heat will create a golden, bubbly top while keeping the interior creamy.

Lay out 4 slices of white sandwich bread or pain de mie on a work surface. Spread a thin, even layer of Dijon mustard (about 1/2 teaspoon per slice) on one side of each bread slice using the back of a spoon or pastry brush.

Place 2 slices of good quality ham (preferably French jambon de Paris or Black Forest ham) on each of 2 bread slices. The ham should cover the bread edge to edge. Top each with 50g grated Gruyère cheese, distributing evenly.

Close the sandwiches with the remaining 2 bread slices, mustard-side down, pressing gently to seal. You should have 2 complete sandwiches. The cheese and ham should be fully enclosed to prevent leaking during cooking.

Spread a generous layer of béchamel sauce (about 3 tablespoons) on top of each sandwich, using a knife or offset spatula to cover the entire surface evenly, right to the edges. The layer should be about 5mm thick.

Sprinkle the top of each sandwich with 30g additional grated Gruyère cheese, covering the béchamel completely. This top layer will become golden and crispy in the oven, creating the signature crust of a croque monsieur.

Transfer sandwiches to the prepared baking sheet. Bake in the preheated oven for 10-12 minutes until the cheese on top is melted, bubbling, and golden brown with dark spots. Watch carefully to prevent burning in the last 2 minutes.

Optional: For extra crispiness, turn on the broiler for the final 1-2 minutes, watching constantly until the top is deeply golden and caramelized. The edges should be crispy while the center remains creamy. Remove immediately when done.

Let the croques rest for 2-3 minutes before cutting. This allows the béchamel to set slightly. Cut each sandwich in half diagonally with a sharp knife. Serve hot, ideally with a simple green salad dressed with mustard vinaigrette and cornichons.