Croque Monsieur Casserole

Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Melt 6 tablespoons of butter. (5 minutes)

In a large bowl, toss English muffin cubes with melted butter and Dijon mustard until evenly coated. Spread the cubes in a single layer on a baking sheet and bake until lightly browned and toasted, about 12-14 minutes. (15 minutes)

In a separate bowl, whisk together eggs, half-and-half, 1 teaspoon of salt, and 1/2 teaspoon of pepper until well combined. Set aside. (5 minutes)

Place half of the toasted English muffin cubes in the prepared baking dish. Distribute half of the ham evenly over the bread, followed by 2 cups of the grated Swiss or Gruyère cheese. (10 minutes)

Repeat layers with the remaining bread cubes, ham, and Swiss cheese. Pour the egg mixture evenly over the casserole, pressing lightly to ensure most of the bread is submerged. Let stand at room temperature for 30 minutes to allow the bread to absorb the liquid. (35 minutes)

Bake the casserole until the egg mixture is absorbed and the top is golden brown, about 45-50 minutes. If the top begins to brown too quickly, cover with foil during the last 20 minutes of baking. (50 minutes)

While the casserole is baking, prepare the cream sauce. In a saucepan over medium heat, melt the remaining 4 tablespoons of butter. Whisk in the flour and cook, stirring constantly, for about 1 minute until smooth. Gradually whisk in the milk until the mixture is smooth. Bring to a boil, then reduce heat to low and simmer, stirring occasionally, until thickened, about 3 minutes. Stir in the remaining 1/2 teaspoon salt, 1/4 teaspoon pepper, and nutmeg. Cook for about 8 minutes on low heat, stirring occasionally, then remove from heat. (15 minutes)

Remove the casserole from the oven and turn on the broiler. Pour the cream sauce evenly over the casserole and sprinkle with the grated Parmesan cheese. Place the casserole back in the oven and broil until the top is bubbly and lightly browned, about 3 minutes. (5 minutes)

Let the casserole stand for 5-10 minutes before serving. Garnish with fresh chives, if desired. (10 minutes)