Extra-cheesy croque monsieur

Start by making a béchamel sauce. Heat 25g butter in a small saucepan over a medium-high heat. When foaming, add the flour and cook, stirring, for 2 minutes. Add the milk a little at a time, stirring constantly, until you have a smooth sauce. Season with salt, pepper and nutmeg; simmer for 1 minute, then take off the heat. Finely chop 2 slices of Emmental and stir into the sauce, then set aside to cool.

Meanwhile, quarter the fennel bulb; cut out and discard the hard core. Slice the quarters as finely as possible and set aside in a bowl of ice-cold water. Preheat the grill to high and set a large frying pan over a medium-high heat.

Spread each slice of bread on one side with the remaining butter and place them buttered-sides down. Spread mustard on four of the other sides and arrange 2 slices of Emmental and 1⁄4 of the ham on top of each. Finish with the remaining bread slices, buttered-side up. Fry the sandwiches, in batches if needed, in the hot frying pan for 2-3 minutes on each side until toasted and golden. Transfer to a large baking tray.

Spread the top of the sandwiches evenly with the cheese sauce. Grill (not too close to the element, so that they colour evenly) for 2-4 minutes until golden. Meanwhile, drain the fennel and pat dry with a clean tea towel, then toss with the oil, lemon zest and juice and reserved fennel fronds. Season and serve with the croque monsieur.