Sift the flour and icing sugar into a bowl. Add the butter and egg yolk, mix well with your fingertips. Add water if necessary, to mix to a soft dough. Cover and place in the fridge for 15 minutes.
Preheat the oven to 200°C . Spray nine mini fluted tartlet tins well with baking spray. Roll out the pastry and use to line the tartlet tins. Prick the bases with a fork, then bake in the preheated oven for 12 - 15 minutes until golden brown. Gently remove the tartlet shells and allow them to cool completely on the cooling rack.
For the filling
Heat the milk until warm. Whisk the egg yolk, sugar, flour, and cornflour together in a mixing bowl until smooth. Add the milk and vanilla extract into the bowl and whisk until smooth.
Pour the mixture back into the pan and stir over a medium heat until boiling. Cook, stirring constantly, for about 2 minutes until thickened and smooth. Let it cool well.
Add the whipping cream and beat until it thickens.
To make the tartlets
Spoon some strawberry jam into each of the cold tartlet shell, then spoon filling on the jam and level the top. When the filling has set slightly, top with sliced strawberries.