Place flour, icing sugar and butter in a food processor and process until mixture resembles fine breadcrumbs. Add egg yolk and water and process until mixture just comes together.
Turn on to a lightly floured surface and knead until just smooth.
Shape into a disc and cover with cling wrap. Place in the fridge for 30 minutes to rest.
Roll out the pastry onto a lightly floured surface to 3 mm thick circles. Line 4 small tart cases with removable bottoms. Line tart cases. Trim edges. Rest in fridge for 30 minutes.
Preheat oven to 200 C. Take tart cases from the fridge. Cut out a circle of baking paper and add baking beans and blind bake for 10 minutes. Remove weights and paper and bake for 10 minutes or until just golden.
Creme Patisserie
Cream egg yolks, sugar and cornstarch together.
Heat milk in a saucepan, bring to the boil. Remove from heat and add little at a time to the egg mixture, until all incorporated.
Return egg mixture back to the saucepan and stirring with a whisk continuously on medium heat until creme patisserie is thick. Remove from heat and add vanilla, then add butter and mix until butter is melted.
Pour into a clean container and cover with cling wrap and allow to cool completely.
Assembling tart. Have fresh berries ready. Add creme patisserie to tart case and smooth top. Decorate top with what ever fresh berries you have.