Preheat the oven to 180C/350F/Gas 4.
Place butter in a pan and melt.
Stir the flour into the butter to make a paste, cook for a minute, then gradually whisk in the milk, a little at a time, until smooth.
Simmer for a few minutes, until thickened.
Take off the heat and stir in 30g cheese until melted.
Grate in nutmeg, stir.
Spread each slice of bread with mustard.
Spread each slice of bread with cheese sauce.
Take two of the bread slices.
Add ham.
Add half of remaining cheese, divide between each slice and place on top of ham.
Top with the rest of the bread, mustard/sauce side up.
Push down sandwich.
Add remaining cheese to the sandwiches.
Add herbs de provence, if required.
Place in oven.
Cook until golden brown.
Serve with gherkins, capers and munch.