1. Start by melting the butter in a pan. Add the flour and stir into the butter. Then gradually add the milk while beating. Let it cook for a couple of minutes to minimize the floury taste. Season to taste with salt, pepper and nutmeg. Remove from the heat.
2. Stir the creme fraiche and the mustard together, and spread the mixture onto the bread slices.
3. Place two slices of ham on two bread slices, followed by slices of Castello Extra Mature Cheddar cheese and close the sandwiches.
4. Fry the sandwich in the butter for about 2-3 minutes on each side. The sandwiches should not brown, so cook them over medium heat.
5. Remove the sandwiches from the pan. Drizzle with the white sauce before topping with grated Aged Havarti. Place under the grill in the oven until the cheese has melted.
6. In the meantime, fry two eggs – one for each sandwich. Place them on top of the sandwiches. Serve immediately.