For the sweet pastry:
Cream the butter and caster sugar together. Beat until the mixture starts to go pale. Combine the 4 egg yolks and the water and beat gradually into the butter mix. Mix the flours and the salt and sift onto the butter mix. Use a rubber spatula to fold the flour in; you are aiming for dough that is homogenous but has been worked as little as possible. Turn the dough onto a floured surface and bring together into a cylinder. Wrap in cling film and chill for at least 30 minutes. Use a third of the pastry to line 6 individual loose bottomed tart tins. Chill the tins and then blind bake at 160℃ for approximately 10 minutes until the pastry is golden brown on the edges. Remove the baking beans and cook for a further 2-3 minutes. When the pastry is a light golden brown, mix the remaining egg yolk with a little water and brush a thin coat onto the pastry. Return to the oven for 1 minute and repeat. Remove from the oven and allow to cool.
For the toffee filling:
Heat the cream to a simmer with the salt and lemon zest. Heat the sugar and golden syrup in a heavy based pan over a medium heat to form a medium caramel. Shake the pan occasionally but avoid stirring. Carefully add the hot cream to the caramel and continue to cook until the caramel is completely dissolved. At this stage you can stir to help the caramel dissolve. Adjust the taste with lemon juice. Warm the milk and dissolve the soaked gelatine in it. Whisk into the toffee sauce.
Pass into a bowl and chill whisking every 15 minutes for an hour. Spread the filling into the pastry cases and chill to set.
For the apple:
Heat the butter in a non stick pan and add the apple, sprinkle over the caster sugar. Cook, turning frequently until well caramelised. Add the apple juice to dissolve the caramel and then reduce completely.
To serve:
Remove the tarts from the fridge 15 minutes before serving. Pile the warm apple onto one side of each tart and quenelle the cream onto the other side. Scatter the Westlands apple blossom over the apple and place a couple of Westlands primula flowers between the apple and the cream.