Pre-heat oven to 200ºC.
To make the pastry, blitz the cold butter, flour and lemon zest until mix looks crumbly. Mix egg and sugar, then add with the water to flour and just mix until dough is combined.
Wrap in cling film and leave in the fridge for at least an hour.
Meanwhile halve and stone your apricots then place on a baking tray cut side up. Sprinkle all over with the light brown sugar then bake them in the oven for 15-20 minutes until they are soft to the point of a knife but not falling apart.
Roll out and line a 25cm loose-bottomed tart tin with the pastry. Chill again.
Once rested prick all over the base with a fork then line with parchment paper and follow with baking beans. Bake blind for 15-20 minutes until the base is just beginning to crisp but has not browned. Remove the beans and allow to cool.
Sprinkle the ground almonds all over the base then top with a layer of apricots. In a large bowl, whisk the eggs and sugar together until light and fluffy. Remove the vanilla seeds from the pod and whisk into the egg mixture along with the whipping cream.
Place the tart onto a baking tray then carefully pour over the custard mixture. Place in the oven for 15 minutes then lower the heat to 180ºC for a further 15-20 minutes when the custard should be set and a lovely golden colour.
Serve with vanilla ice cream or whipped cream.