Croque Forestier

Instructions

1. Prepare the mushrooms
   In a large skillet, melt 2 tablespoons of butter over medium-high heat. Add the shallots and cook for 2 minutes until softened. Add the garlic and mushrooms, cooking until the mushrooms are golden brown and have released their moisture, about 7-8 minutes. Season with salt, pepper, and fresh thyme. Set aside.
2. Make the béchamel sauce
   In a saucepan, melt the remaining tablespoon of butter over medium heat. Add the flour and whisk constantly for 1-2 minutes to make a roux. Gradually pour in the warm milk, whisking continuously to prevent lumps. Cook for 3-4 minutes until the sauce thickens. Remove from heat and stir in half of the grated Gruyère, nutmeg, salt, and pepper.
3. Assemble the sandwiches
   Preheat your oven to 400°F (200°C). Lightly butter one side of each bread slice. Spread Dijon mustard on the unbuttered sides of 4 slices. Divide the mushroom mixture evenly among these 4 slices, then top each with about 2 tablespoons of the béchamel sauce.
4. Complete the assembly
   Sprinkle some of the remaining Gruyère over the béchamel on each sandwich. Close with the remaining bread slices, buttered side up. Place the sandwiches on a baking sheet.
5. Bake to perfection
   Spoon the remaining béchamel sauce over the top of each sandwich and sprinkle with the remaining Gruyère. Bake in the preheated oven for 10-12 minutes until the cheese is melted and golden brown, and the sandwiches are heated through.
6. Serve
   Remove from the oven and let cool for 2 minutes. Garnish with additional fresh thyme if desired, and serve hot, accompanied by a simple green salad if you wish.