Croque Monsieur

How to make it

1. Melt the butter for the béchamel in a heavy-bottomed saucepan over medium heat, and whisk in the flour. Let the roux bubble for 2 minutes, until it smells lightly nutty and is still completely pale.
   Chef's tip Those two minutes cook out the raw-flour taste while the roux stays blond. Let it take colour and it loses thickening power, so you'd need more flour for the same body.
2. Add the cold whole milk a little at a time, whisking constantly so the flour doesn't clump. Let the béchamel cook through for 5-6 minutes, until it's thick enough to coat the back of a spoon in an even layer.
   Chef's tip Cold milk against the hot roux buys you time to disperse the flour before it swells. The sauce stays thin, then thickens quite suddenly as it nears a simmer — keep whisking through that moment.
3. Take the pan off the heat and season the béchamel with salt, white pepper, and the freshly grated nutmeg. Go easy on the salt, since both the gruyère and the ham will salt the dish heavily afterward. It should taste clearly of milk and nutmeg, not of salt.
   Chef's tip Nutmeg and white pepper lose their aroma in a boiling sauce, which is why you season off the heat. Give it a stir a few times while the bread toasts — left standing, the sauce forms a skin that turns into lumps in the layer.
4. Preheat the oven to 220°C.
5. Butter one side of all eight slices of pain de mie with the softened butter. Toast the slices butter-side down in a dry skillet over medium heat for 4-5 minutes total, until lightly golden. The crust holds the bread together once the béchamel soaks in.
   Chef's tip Keep the pan at a steady, quiet sizzle. Too hot and the butter's milk solids brown before the surface has dried, leaving a soft slice that the béchamel soaks straight through.
6. Place four of the toasted slices golden-side up on a baking sheet. Spread a thick layer of béchamel on each, reserving enough béchamel to cover the top of all four sandwiches. Lay a slice of cooked ham on top and sprinkle half of the grated gruyère over it. Place the last four slices on top golden-side down, and press lightly so the layers hold together.
7. Spread the remaining béchamel over the top of the four sandwiches all the way to the edges, so no bare bread is exposed and burns. Sprinkle the last of the gruyère evenly over the top, until it's completely covered.
8. Bake them in the middle of the oven for 10-12 minutes, until the cheese has melted completely into the béchamel and is bubbling around the edges. ⏱ 10 min · passive
9. Turn on the broiler and gratiné the croque monsieurs for 2 minutes, until the top is mottled golden brown. Stay by the oven, since the last few seconds are the difference between golden and burnt.
   Chef's tip Put the sheet on the top rack so the tops sit close to the broiler element; further down, the cheese dries out before it mottles. The mottling rarely comes evenly — turn the sheet halfway around as the first spots darken.
10. Take the pan out and let them rest for 2 minutes, so the bubbling béchamel settles and doesn't run out when they're lifted. ⏱ 2 min · passive
11. Lift each croque monsieur whole onto a flat plate with the cheese crust facing up, and serve immediately while hot. They're eaten with a knife and fork: cut down through the crisp cheese crust so the melted layer inside comes up with it.