About this recipe

The ultimate French bistro sandwich — thick slices of bread layered with smoky ham and nutty Gruyère, smothered in a rich, silky béchamel, then broiled until golden and bubbling. This classic, well-tested home version is approachable, reliable, and utterly satisfying. It's the kind of sandwich that turns an ordinary lunch into a small celebration.

Instructions

1. 1

   Melt the butter in a small saucepan over ^[medium heat]. Once it foams, add the all-purpose flour all at once and whisk constantly for 1–2 minutes until the mixture smells slightly nutty and looks pale golden — this cooks out the raw flour taste.

2. 2

   Gradually pour in the milk warmed in a slow, steady stream, whisking vigorously the entire time to prevent lumps. Continue whisking over ^[medium heat] for 3–4 minutes until the sauce thickens enough to coat the back of a spoon. Remove from heat and season with salt, white pepper, and a pinch of nutmeg. Set aside.

3. 3

   Preheat your oven to ![400°F]. Line a baking sheet with aluminum foil. Lay all 4 bread slices on the baking sheet and spread one side of each slice lightly with softened butter. Bake for 5 minutes until just lightly toasted on top.

4. 4

   Remove from the oven. Flip all 4 slices so the toasted sides face down. Spread a thin layer of Dijon mustard on the untoasted (now top-facing) side of all 4 slices.

5. 5

   Sprinkle about a quarter of the grated gruyere cheese evenly over the mustard side of 2 slices (these will be the bottoms). Divide the ham evenly over those same 2 slices, folding it to fit neatly. Close the sandwiches by pressing the remaining 2 slices on top, mustard-side down.

6. 6

   Spoon the béchamel generously over the top of each closed sandwich, spreading it all the way to the edges with a spatula. Divide the remaining gruyere cheese evenly over the béchamel-topped sandwiches.

7. 7

   Bake at ![400°F] for 8–10 minutes until the béchamel is set and the bread is heated through. Then switch the oven to ^[broil (high)] and broil for 2–3 minutes, watching closely, until the top is deeply golden, bubbly, and spotted with brown. Serve immediately.