Croque Monsieur Gratin
A French bistro classic turned into an oven gratin: sourdough layered with ham and nutty gruyere, soaked in a quick mustard bechamel, then baked until the top is golden and bubbling.
- Total
- 33 min
- Prep 12 · Cook 21
- Serves
- 1
- Difficulty
- Easy
You'll practice: Making a roux · Simmering
- Standard
- Savory
- French
- Crispy
- Oven
Instructions
-
Heat the oven to 220°C. Grate the gruyere on the coarse side of a box grater.
~4 min
Coarse grating melts evenly and gives the cheese a nutty, bubbly finish rather than a dense, greasy layer.
-
Melt the butter in a small saucepan over medium heat. Whisk in the plain flour and cook for 1 minute until it smells toasted but has not browned.
~1 min
Cooking the flour in butter makes a roux, which thickens the milk and removes the raw flour taste.
Making a roux Cook the flour and butter for about a minute until it smells toasty but stays pale; browned roux loses thickening power and tastes bitter.
-
Pour in 250 ml milk in a steady stream, whisking constantly, then whisk in the dijon mustard, 0.25 tsp salt and 0.25 tsp black pepper. Simmer for 3 minutes, whisking, until the bechamel coats the back of a spoon.
~3 min
Simmering hydrates the flour and reduces liquid so the bechamel clings instead of soaking the bread.
Let the bechamel thicken fully before assembling; a loose sauce will soak the sourdough into mush instead of holding a bubbling gratin.
Simmering Keep the bechamel at a gentle bubble, whisking constantly, until it coats the back of a spoon; boiling hard can scorch it.
-
Spread a thin layer of bechamel in the baking dish. Layer 2 slices of sourdough, 2 pieces of ham, a third of the gruyere, then repeat with the remaining sourdough, ham and another third of the gruyere.
~3 min
-
Pour the remaining bechamel over the top and scatter the last of the gruyere evenly across the surface.
~2 min
Covering the top with bechamel and cheese insulates the bread so it bakes into a tender, saucy gratin.
-
Bake for 18-20 minutes until the cheese is melted, the top is deep golden and the edges bubble. Rest 2 minutes before cutting into 2 portions.
~20 min
Resting lets the molten cheese and sauce set slightly so portions hold together when cut.
For a deeper golden top, switch to the broiler for the final 2 minutes, watching closely so the gruyere browns without burning.