Melt the butter in a saucepan and add flour. Cook off for about 30 seconds to one minute.
Pour in the milk and whisk until smooth and starting to thicken. Reduce heat to medium low and cook for two minutes while stirring.
Add mustard and season well with Man Grind. Remove from the heat. You should have a fairly thick béchamel sauce.
Cut the croissants in half horizontally. Spread a little béchamel on each half of the croissant and place a couple of slices of ham and a slice of cheese on top. Repeat with all the croissants. You should have some béchamel left over for the top.
Cut the filled croissants in half and arrange in a shallow casserole or baking dish.
Whisk together 4 eggs and 1/4 cup of milk and season with Man Grind. Pour over the filled croissants and give them a gentle push or jiggle to encourage them to soak up a little or the egg on the bottom.
Dollop any remaining béchamel ontop of the croissants and add a little additional grated cheese if you like.
Bake for 25 minutes at 180C Fan Bake or until golden and the egg has puffed up. Keep a fairly close eye on it because the croissants can burn easily.