Heat the grill to medium–hot.

Set a medium saucepan over medium heat. Add the butter and when it’s bubbling away, add the flour and stir it in. Cook the flour for a minute or so, stirring regularly, then pour in the milk. Whisk the milk until it comes up to the boil and the sauce begins to thicken; about 3–4 minutes. Add the cheese, mustard, chives and parsley. Stir the sauce for a few minutes, until the cheese is melted and the sauce is nice and smooth. Season well with salt and pepper, then remove from the heat and set aside.

Lightly toast the buttered bread on both sides under the hot grill. Remove the grill pan from the grill and divide the ham equally between the six toasts. Spoon over the thick sauce and scatter over a handful of finely grated cheese. Place the tray back under the grill and cook until the sauce is bubbling and golden in places and the ham is piping hot. Serve straight away.