5 tablespoons unsalted butter
1 tablespoon flour
1 cup milk
1/4 teaspoon salt
Pinch of freshly grated nutmeg
1 cup grated Gruyere cheese
4 slices white bread
2 teaspoons Dijon mustard
3 ounces best-quality deli ham, thinly sliced
2 large eggs
Ground pepper to taste
Preheat the broiler with the rack in the top position. In small saucepan, melt 2 tablespoons butter over high heat. Whisk in flour and cook until lightly golden. Add milk and salt and whisk constantly until mixture thickens, about 2 minutes. Remove from the heat. Stir into the sauce the nutmeg and half the cheese.
Lay the slices of bread on a baking sheet. Divide the Dijon between 2 slices and top with ham. Divide half of the bechamel between the remaining 2 bread slices and top with remaining cheese. Close the sandwiches.
Melt 2 tablespoons butter in a large skillet over medium heat. Add sandwiches and cook both sides until bread is golden brown and the cheese is melted, about 3-4 minutes.
Return sandwiches to the baking sheet, top with remaining bechamel, and place under the broiler until bubbly, about 2 minutes. Meanwhile, melt remaining butter in the same skillet over high heat. Fry eggs, sunny side up, for about 2 minutes. Top sandwiches with fried egg, season with black pepper, and serve immediately.
Recipes shared from: http://www.marthastewart.com/353224/croque-madame?czone=food/lunch-recipes/sandwich-recipes¢er=856055&gallery=853317&slide=352654