Ingredients:

  • 4 Tbsp Unsalted Butter (55 g), for the roux
  • 1/4 cup All-Purpose Flour (45 g)
  • 2 cups Whole Milk, warmed (500 ml)
  • 1/2 cup Gruyère Cheese, grated (50 g), reserved for the Béchamel sauce
  • 1 tsp Sea Salt
  • 1/4 tsp Freshly Ground Black Pepper
  • Generous pinch Freshly Grated Nutmeg
  • 8 slices Sturdy Sliced White Bread (e.g., Pain de Mie)
  • 2 Tbsp Unsalted Butter, softened (30 g), for buttering the bread
  • 8 slices Thinly Sliced Ham (Approx. 200 g)
  • 5 cups Gruyère Cheese, grated (150 g), for filling and topping
  • 4 tsp Dijon Mustard (Optional)

Instructions:

  1. Preheat the oven to 200°C (400°F). Line a baking sheet with parchment paper. Grate the Gruyère, dividing it into the amounts needed for the Béchamel (50g) and the assembly (150g). Gently warm the whole milk in a separate pan or microwave and keep it warm.
  2. Make the Roux: Melt 4 Tbsp of unsalted butter in a medium saucepan over medium heat. Whisk in the flour until a thick paste (the roux) forms. Cook for 1–2 minutes, stirring constantly, until the paste smells slightly nutty.
  3. Add Milk: Gradually pour in the warm milk, whisking vigorously the entire time to prevent lumps. Start with a small amount until the mixture is smooth, then add the rest slowly.
  4. Thicken and Season: Bring the sauce to a gentle simmer, stirring frequently, until it thickens and coats the back of a spoon (about 5-8 minutes). Remove the sauce from the heat.
  5. Finish the Sauce: Stir in the salt, pepper, a generous pinch of nutmeg, and the 50g of Béchamel Gruyère. Taste and adjust seasoning. Keep the Béchamel warm.
  6. Prep the Bread: Lightly butter one side of all 8 slices of bread. Place the slices butter-side-down onto a work surface. Spread a light layer of Dijon mustard (if using) on the unbuttered side of all 8 slices.
  7. Build the Sandwich: Lay a base slice of bread (mustard side up). Sprinkle a thin layer of the remaining Gruyère (about 1/4 cup total for all four bases). Add 2 slices of ham. Top with a generous scattering of Gruyère (about 1/4 cup total). Place the top slice of bread (mustard side down) onto the sandwich.
  8. Coat and Top: Place the four assembled sandwiches onto the prepared baking sheet (butter side facing out). Pour or spoon the warm Béchamel evenly over the top of each sandwich, ensuring full coverage.
  9. The Finale & Bake: Sprinkle the remaining grated Gruyère over the Béchamel layer. Bake in the preheated oven (200°C / 400°F) for 10–12 minutes, or until the sauce is bubbly and the edges are golden brown.
  10. Broil for Colour: Switch the oven to the broiler (grill) setting for 1–2 minutes, watching carefully, until the cheese topping is deeply golden and caramelized. Allow the sandwiches to rest for 2 minutes before serving.