Croque-monsieur Recipe

Prepare shallot

Peel and finely mince 1 shallot. Set aside.

Sweat shallot

In a medium saucepan, melt 3 tbs unsalted butter over medium-low heat. Add the minced shallot and cook gently for 3–4 minutes until softened and translucent but not browned.

Make roux

Raise heat to medium and sprinkle in 3 tbs all-purpose flour. Stir constantly with a whisk or wooden spoon for 1.5–2 minutes to cook the raw flour taste, forming a blonde roux with the shallot. Do not let it darken.

Deglaze (optional)

If using, pour in 2 tbs dry white wine and whisk until mostly evaporated, about 30–45 seconds. This step adds brightness but can be omitted.

Add milk and thicken

Gradually pour in 2 cups whole milk while whisking to prevent lumps. Increase heat to medium and simmer gently, whisking frequently, until the sauce thickens to a coating consistency (about 4–6 minutes).

Season and finish

Remove from heat. Stir in 1 cup grated gruyère until melted and smooth (reserve a few tablespoons for topping if desired). Season with 1 tsp salt, 1 tsp pepper, and 1 tsp freshly grated nutmeg. Taste and adjust seasoning. Keep warm; if it thickens too much, thin with a splash of milk.

Preheat

Preheat oven to 425°F (220°C). Line a baking sheet with parchment or lightly butter it.

Prepare bread

Spread about 1/2 tbs of stone-ground or Dijon mustard on one side of 4 brioche slices. (Total mustard quantity above accounts for both sandwiches.)

Build sandwiches

On the mustard-spread side of each of the 4 slices, place two slices of ham (or enough to cover) and a generous sprinkle of the grated gruyère (about 1/4 cup per sandwich). Spoon a heaping 1/4 cup of the warm shallot béchamel over the cheese/ham layer (reserve remaining béchamel for topping). Top with the remaining brioche slices, pressing gently to adhere.

Butter and top

Lightly butter the outer faces of each sandwich with the remaining unsalted butter (about 1/2 tbs per face). Place sandwiches on the prepared baking sheet, buttered side up.

Bake and brown

Bake in the preheated oven 6–8 minutes until the tops are lightly golden. Remove from oven and spoon remaining shallot béchamel over the top of each sandwich, then sprinkle with the reserved grated gruyère (about 1–2 tbs each). Return to oven and bake 4–6 minutes until cheese is bubbly. For a deeper brown crust, switch to broil for 1–2 minutes, watching closely to avoid burning.

Rest and serve

Let sandwiches rest 1–2 minutes on the baking sheet. Slice each sandwich in half on the diagonal and serve hot.