To make the sauce, heat the milk in a saucepan with the onion, cloves and bay leaf. When boiling, turn off the heat and leave to infuse for 30 mins, then strain.

Melt the butter in another pan and add the flour. Cook for 4-5 mins until sandy. Gradually whisk in the milk, then cook over a medium heat, stirring, until you have a thick sauce. Stir in the mustard and season. Set aside to cool. Can be made up to two days ahead.

Heat oven to 180C/160C fan/gas 4. Butter a baking tray large enough to fit 3 slices of bread, then butter and toast the bread, and make 3 sandwiches with 2 slices of ham and cheese in each. Spread the white sauce on top, and make a small well in the sauce on each sandwich. Crack the eggs into the wells, then scatter over the parmesan. Bake for 20 mins or until the whites are just set.