Marbled peppermint and chocolate soufflés

PASTRY CREAM: In a bowl, whisk egg yolks with about a third of the castor sugar until pale in colour and mixture makes a thin ribbon when whisk is lifted. Sift in flour and mix in thoroughly.
In a saucepan, bring milk to boil with remaining sugar. Pour onto egg mixture, stirring continuously to make a custard.
Pour back into pan, add vanilla essence and bring to boil over very gentle heat, stirring continuously until thickened. If using a vanilla pod (see tips), remove.
Transfer pastry cream to a bowl. Dot surface with a few flakes of butter or dust lightly with icing sugar to prevent a skin forming as it cools down.
PREPARING DISHES: Grease insides of 5 medium-sized or 10 small ramekins with softened butter (or spray with non-stick cooking spray). Place 30 g of the castor sugar in 1 dish and rotate to coat butter on surface completely with sugar. Tip excess sugar into next dish and repeat process. Repeat for remaining dishes.
Set oven to 190 ºC and place a baking sheet in it to heat.
ASSEMBLING SOUFFLÉS: Place pastry cream in a wide-mouthed bowl and warm to tepid, or stand bowl in a baking pan of hot water (bain-marie) set over moderate heat. Stir in peppermint liqueur.
Whisk egg whites until soft peaks form, then add remaining 150 g castor sugar and whisk into semi-firm peaks. Using a whisk, mix one third of beaten egg whites into pastry cream, then carefully fold in remainder with a slotted spoon or spatula.
Scatter in the chopped chocolate. Pour mixture into prepared dishes and smooth surface with a palette knife.
Place ramekins on the heated baking sheet and bake for 8 to 12 minutes, or until risen and lightly golden on top.
As soon as soufflés comes out of the oven, place a mint sprig on each and dust with a light veil of icing sugar. Place each dish on a plate lined with a paper doily, and serve immediately.