Start by making the creme patisserie custard filling. Heat the whole milk with the seeds from a vanilla pod in a pan until it reaches boiling point. Then take it off the heat and pour it into a jug
Using an electric mixer whisk up the egg yolks with the caster sugar until pale and thick. Add the cornflour and mix it in, then pour the warm milk in with the mixer still going
Pour the mixture back into the pan and heat it at a medium-high heat whilst continously stirring. When it starts to thicken, whisk it to keep it smooth and stop any lumps
Sieve it required to remove any lumps, then put it in a bowl and covered it with cling film. Make sure the cling film is touching the creme patisserie so that a skin doesn't form on it. Leave it in the fridge overnight to cool
To make the pastry rub the butter into the plain flour until it resembles breadcrumbs
Add the eggs and mix to form a dough. Wrap it in cling film and chill it in the fridge for 30 minutes
Roll out the pastry and line a 23cm tart tin. Prick it all over with a fork
Line the pastry with baking paper then pour in baking beans (or dry rice if you don't have them) bake it on 180C/106C Fan/350F/Gas Mark 4 for 15 minutes
Remove the baking beans and baked it again for 10-15 minutes until the bottom is fully cooked and it is golden brown all over
When the tart case is fully cool fill it with the creme patisserie and smooth it out
Slice up the nectarines and arranged them in circles on top, then place the billberries in the gaps
To glaze the tart, warm up the apricot jam in a pan. Sieve it to remove any lumps, and use a pastry brush to generously brush it all over the tart