How long does it take to make Croque Monsieur?

Bake at 200–220°C (390–430°F) for 10–15 minutes, until the topping is golden and the cheese is bubbling.

34 minTotal

16 minActive time

18 minSetting

#	What to do	How long
1	Melt the butter in a pot over medium heat, add the flour and stir 1–2 minutes	2 min
2	Gradually add the milk, whisking constantly, and cook 5–8 minutes	6 min
3	Season with salt and Nutmeg	1 min
4	Preheat the oven to 200°C (390°F)	12 min
5	Spread béchamel on half of the bread slices and top with the yellow cheese	1 min
6	Close each sandwich with another slice of bread and place on a baking sheet lined with parchment paper	1 min
7	Spread the rest of the béchamel over the sandwiches	1 min
8	Bake 10 minutes	10 min

Add the milk slowly, whisking constantly, so no lumps form. For lasagna, the common ratio is about 7 g flour per 100 ml milk (4 tablespoons flour to 2 cups): more flour gives a thick béchamel, for moussaka; less flour gives a soft béchamel, for a sauce.
Put things in the oven only once it's reached temperature, after the heating light has gone off: an oven that hasn't reached temperature changes baking times, and the bake burns outside or stays underbaked.
The béchamel on top of the sandwich keeps the bread from drying out in the oven, and the grated cheese on it browns into a crust.

Check by the cue (until…), not just the clock: every oven bakes a little differently.

A hot sandwich with cheese (usually Emmental or Gruyère) and ham; in Israel it is usually served without the ham.
Béchamel of butter, flour and milk with nutmeg, salt and pepper: a spoonful of béchamel on the bottom slice, cheese and ham, a second slice, and another spoonful of béchamel and grated cheese on top.
A croque monsieur served with a fried (or poached) egg on top is called a croque madame.