A Croque Monsieur is a French toasted ham and cheese sandwich bound with creamy béchamel sauce and melted gruyère. This bistro classic delivers restaurant-quality results at home with just butter, flour, milk, and quality cheese.
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In a small saucepan, melt the butter over medium heat. Add the flour and whisk for 1 minute to obtain a smooth roux. Gradually pour in the milk, whisking constantly to avoid lumps.
Let cook for 5 to 7 minutes, stirring often, until the sauce thickens and coats the back of a spoon. Season with salt, pepper, and a pinch of nutmeg.
Cover with plastic wrap pressed directly on the surface to prevent a skin from forming and set aside.
Preheat the oven to 410°F (210°C, convection) or 425–445°F (220–230°C, regular oven).
Lightly toast the slices of bread in a toaster. Spread a thin layer of Dijon mustard on one side of the bread.
Spread a little béchamel, add a slice of ham, and sprinkle with cheese.
Close with another slice of toasted bread. Spread the top with the remaining béchamel and sprinkle with the rest of the cheese.
Place the croques on a baking sheet lined with parchment paper. Bake for 15 to 20 minutes, until the top is nicely golden and gratiné.
Remove from the oven and enjoy immediately, served with a green salad.
Store leftovers in an airtight container in the fridge for up to 2 days. Reheat in a skillet over medium heat until warmed through and cheese re-melts, about 2–3 minutes per side.
Gruyère is traditional, but emmental and comté work equally well. Avoid pre-sliced cheese; grate your own for better melting.
Yes. Prepare it up to 2 days ahead, cover, and refrigerate. Reheat gently over low heat, adding a splash of milk if it thickens too much.
No. The recipe lists it as optional. Omit it if you prefer a milder flavor or have a mustard aversion.
Use a skillet or griddle over medium heat with a light butter coating. Toast until the bread is golden and the cheese melts through, about 3–4 minutes per side.
Freeze assembled (unbaked) sandwiches wrapped in foil for up to 1 month. Thaw in the fridge and toast as directed; add 1–2 extra minutes to cooking time.
