The best ham and cheese sandwich in the world. Stringy oozy cheese, salty ham, mustard and good bread toasted in butter. What more could you require from a sandwich.
Melt butter in a small saucepan. When butter has melted stir in the flour with a wooden spoon, allow to cook for a couple of minutes to cook flour.
Remove the pan from the heat, switch the wooden spoon for a whisk. Whisk the milk into the pan, about a tbsp at a time. When mixture has loosened and become more runny you can add the milk more generously. Return to the heat and stir until thickened. Turn off the heat season with salt pepper & nutmeg. Stir through the grated cheese until melted. Then set aside until required.
Using the Dijon, butter one of your slices of bread. Layer with a slice of ham, cheese, ham and cheese. Sandwich together with the other slice of bread. Repeat to make the second sandwich.
Heat half the butter and oil in a heavy based pan (that is suitable to go under the grill) over a low heat. When melted and hot add the sandwiches, cook on the first side until toasted and browned. Add the remaining butter and oil, then flip over the sandwich and let it cook until toasted.
Turn the heat off under the pan and spoon the béchamel sauce over the sandwiches. Top with remaining cheese then place under a hot grill until cheese is blistered and slightly bronzed. Remove to a cutting board and cut the sandwich in half.