Croque Monsieur Truffe « Comme Fabienne » Recipe

Prepare bread and spread

Preheat oven to 425°F (220°C) with rack in middle. Lightly butter one side of each of the 8 slices of bread; these will be the outside surfaces for grilling. On the unbuttered side of four slices, spread approximately 1/2 tablespoon black truffle paste evenly, leaving a small border.

Assemble sandwiches

On each of the four truffle-pasted slices, distribute about 1/2 cup grated Gruyère (reserve the 1 cup for topping), then top with two slices of ham folded to fit. Spread a thin layer (about 1 tablespoon) of room-temperature butter on the inside of the remaining four bread slices and place them butter-side-up as the top pieces to close the sandwiches. Press gently to compact.

Initial toasting

In a large skillet over medium heat, add 1 tablespoon butter. When it foams, add two sandwiches, buttered side down, and cook 2–3 minutes until golden, pressing gently with a spatula. Flip and toast the other side 1–2 minutes just to set the crust (they will finish in the oven). Transfer to a rimmed baking sheet, buttered side up. Repeat with remaining sandwiches.

Make the roux

In a small saucepan over medium heat, melt 3 tablespoons unsalted butter. Add 3 tablespoons all-purpose flour and whisk continuously for 1–2 minutes until the raw flour smell is gone and the roux is pale and bubbling but not browned.

Finish béchamel

Gradually whisk in 2 cups warm whole milk, a little at a time, ensuring no lumps form. Bring to a gentle simmer, whisking constantly, until the sauce thickens to a coating consistency (about 4–6 minutes). Reduce heat to low, stir in 1 teaspoon Dijon mustard, 1 teaspoon grated nutmeg, 3/4 teaspoon sea salt and 1/2 teaspoon freshly ground black pepper. Taste and adjust seasoning. Remove from heat and whisk in 1 teaspoon black truffle oil (or 1 teaspoon diluted truffle paste) and 2 tablespoons of the grated Gruyère so the sauce becomes glossy and cohesive. Keep warm.

Assemble with béchamel

Spoon about 2–3 tablespoons of the truffled béchamel onto the top surface of each pre-toasted sandwich (the buttered side up). Spread evenly with the back of the spoon to cover the bread. Sprinkle the reserved 1 cup grated Gruyère evenly across the four sandwiches, pressing lightly so the cheese contacts the béchamel.

Gratinée

Increase oven temperature to broil (or keep at 425°F/220°C if using a conventional oven). Place the baking sheet with sandwiches under the broiler about 4–6 inches from the heat source. Broil for 2–4 minutes, watching constantly, until the béchamel bubbles and the cheese forms a deeply golden, slightly blistered crust.

Rest and garnish

Remove the sandwiches from the oven and let rest 1–2 minutes. If using fresh truffle, shave or thinly slice about 1/2 tablespoon and scatter over the hot gratinée. Alternatively, finish with a small drizzle (about 1/4 teaspoon) of truffle oil per sandwich for aroma. Slice each sandwich in half on the diagonal and serve immediately.