Preheat oven to 180 degrees C. Grease and flour a tart tin with a removable base.
In a food processor, combine all dough ingredients into a smooth ball. Use to line the tart tin. The dough is fragile, you'll have more luck pressing it out than rolling it. Prick all over with a fork.
Bake dough 20-25 minutes or until just golden. Remove and let cool completely.
In a bowl, combine water, lemon zest and juice, egg yolks, sugar, cornflour and butter. Whisk until smooth and sugar has dissolved. Pour into a saucepan and bring to a gentle simmer, stirring constantly until thickened and bubbly. Let cool.
Pour the cold lemon cream into the tart base, spread smooth then chill in the fridge until firm.
Once cool, arrange the berries over the top. Sprinkle with a little icing sugar.