Croque monsieur is French for "crunchy mister". This is not crunchy nor is it a man, but it is an exquisite rhapsody in beige. Oozing, mustardy bechamel. Equally oozing emmental. Salty ham. Soft potatoes. Delicious garlic butter. What's not to love?
Preheat the oven to 180°C. To kick things off, use a mandolin or sharp knife to cut the potatoes into 4mm slices. Toss these in a bowl with the olive oil and salt, then spread them in an even layer on a couple of lined baking sheets. Bake until completely soft, around 20 to 30 mins.
Meanwhile, make the bechamel. Heat the butter in a saucepan until foaming then add the plain flour. Whisk for around 30 seconds, then add the mustard and salt. Slowly pour in the milk, thoroughly whisking between each addition, until you have a thick, smooth sauce.
Mix the mash, whole egg, butter and salt and place in a starred piping bag.
In a lined 23 cm baking tray, spread a layer of concentric overlapping potatoes on the bottom and around the sides.
Top with a layer of ham, followed by a few big spoonfuls of bechamel and grated emmental followed by another layer of potatoes. Repeat for 3 layers (or more if you have a deeper tin and more ham and cheese), finishing with a final layer of potatoes.
Pipe the mash over the top, then bake in the oven at 180°C for around 40 minutes to an hour.
Leave to sit for around 20 minutes before serving,
