Grease 4 individual ramekins with the butter and set aside.
Heat the oven to 200C (180C fan), gas 6.
Put the milk, sugar, vanilla extract, orange zest, flour and salt in a small pan and slowly bring to a boil, stirring frequently.
Plunge the base of the pan in a sink of iced water and let cool.
Beat the egg yolks and stir into the cooled cream with the orange juice and orange liqueur.
Whisk the egg whites until they form stiff peaks and fold in the orange cream mixture.
Divide between the greased ramekins and bake for 15 - 20 minutes or until the souffles are risen.
Serve immediately garnished with sifted icing sugar and orange zest.