place the milk, onion, peppercorns and bay leaf in a pot and heat to just before boiling point

remove from the heat and infuse for 30 minutes

pour the milk through a sieve

in a saucepan melt the butter and then add the flour

stir until golden in colour

add one ladle of the milk and mix until smooth

add another ladle of milk and mix until smooth

add the rest of the milk and keep on a low heat for 30 minutes

add the cream and mix until smooth

remove from the heat and add the mustard and cheese

season to taste