Croque-Monsieur

Melt butter in a small saucepan over medium heat. Add flour all at once and stir vigorously with a wooden spoon or whisk for 90 seconds — the roux should turn pale blonde and smell faintly nutty, not raw. Gradually pour in warm milk, whisking constantly to prevent lumps. Stir over medium heat until the sauce thickens to a consistency that coats the back of a spoon heavily. Season with salt, white pepper, and a generous grating of nutmeg.

Spread butter on one side of each bread slice. Toast buttered-side down in a dry skillet over medium heat for 2–3 minutes until golden and fragrant. This step is often skipped in shortcuts, but pre-toasting prevents the bottom bread from going soggy under the wet béchamel. Remove from heat.

Spread a generous layer of béchamel on the untoasted side of the bottom bread slice. Lay ham slices to cover completely. Add a layer of grated Gruyère. Place the second slice on top, toasted side up. Spread more béchamel over the top of the sandwich — this is the defining move of the croque-monsieur — and pile the remaining Gruyère on top.

Place the assembled croque on a baking sheet under a hot broiler set to high, positioned 15 cm from the element. Broil for 3–5 minutes, watching constantly, until the Gruyère on top is bubbling, golden-brown, and developing dark spots. The edges of the béchamel should be caramelizing. Serve immediately — the crust is best in the first 90 seconds.