For the pastry, place the flour, butter and sugar into a bowl, gently and quickly rub into the consistency of bread crumbs. If using a food processor, blend to this consistency. Drizzle in the egg yolk and use a knife to mix through till the crumb starts to come together. (If using a food processor blend the egg into the mix for a few seconds till the crumb combines.) If the mixture is too dry you can add small amounts of egg white to the bowl or processor and blend till the crumb comes together.
Form the pastry into a block and chill in a fridge for 20 minutes until hard.
Grease a 25cm/10in tart tin then dust it with flour.
Using a rough edged grater grate the cold pastry into the tart tin. Push the pastry into the corners then grate more pastry and firm down onto the base of the tin until about 6mm/¼in deep. Place in the fridge for approximately 20 minutes while you make the pastry cream.
To make the pastry cream, place the egg yolks and caster sugar in a bowl. Whisk until thick and pale in colour then stir in the flour and corn flour.
Place the milk in a saucepan, add a pinch of salt. Score the vanilla pod down the length with a knife and add it to the milk and bring to the boil. Remove from the heat and leave the mixture to infuse for 10 minutes.
Remove the vanilla pod and return the milk to the heat. Bring to the boil and then slowly add the hot milk to the egg mixture whisking all the time. Pour the mixture back into the pan and reduce the heat to low. Whisk constantly and bring to the boil again. After around two minutes the mixture should thicken. Pour into a cold bowl to stop the cooking process.
Whisk the cream until soft peaks form when the whisk is removed, and then fold it into the pastry cream. Add the whisky to the mixture and chill it in the fridge.
To blind bake the pastry, Preheat the oven to 180C/350F/Gas 4. Remove the pastry and tart tin from the fridge. Cut a piece of greaseproof paper or baking parchment that is larger than the tin and scrunch into a ball and open out again so that it’s soft and less rigid. Place the paper into the pastry case and gently fill with dried pulses or baking beans. Blind bake the pastry case in the oven for around 20 minutes until it feels dry to the touch. Remove the parchment/greaseproof paper and beans, brush the pastry with egg white and return to the oven for 5-8 minutes to seal the pastry.
To assemble the tart, spoon the cooled pastry cream into the pastry case. Top with raspberries and blackberries. Dissolve the apricot jam into the just boiled water. Using a pastry brush, gently coat the fruit with the glaze, sprinkle with toasted almonds and dust with icing sugar.
To serve remove the outer ring of the tin. Easy the base off with a knife and slide onto a plate or cake stand.