Mix pastry ingredients till crumbly, add ice water into it and knead to become a dough.
Shape it into ball and wrap it with aluminium foil. Put dough in freezer for about 15 minutes.
Roll the pastry dough flat into about 3mm thickness between two plastic sheets. Use a round cutter to cut dough and place it into tart mould.
Press the dough evenly in mould and trim excess dough with a sharp knife.
Prick some holes with a fork to release air from the pastry and place the tart moulds in the freezer for another 10 mins or for a day or two.
Take out tart moulds from freezer, line with aluminium foil and blind bake medium size tarts for 30 minutes and mini size tarts for 20 minutes at preheated oven 180C. Remove aluminium foil immediately from tart moulds after baked and leave tart pastry to cool.
Wash and scrub sweet potato and steam at high heat till soft.
Remove skin and put sweet potato in a food processor together with sugar, butter, egg yolk and whipping cream and blend till fine paste, set aside. (measure 200g for making sweet potato cream)
200g Sweet potato paste
Making Sweet Potato Cream
Whip cream with sugar on medium speed until stiff peaks form,
Add sweet potato paste into the whipping cream and mix to combine to sweet potato cream.
Add sweet potato cream into a piping cream and pipe into tart shells.
Chill for 30-60 mins to let cream set.
Spoon the remaining sweet potato paste into a piping bag and pipe on top of sweet potato cream.
Chill sweet potato tarts and dust some icing sugar or snow powder before serve.
Sweet potato tarts can be also served immediately.