Heat berries, 15g sugar, and water in a pan for five minutes until softened and cool.
Gently heat cream, milk, and vanilla seeds in a bowl over a pan of simmering water.
Beat egg yolks and 80g sugar until fluffy, then stir in the warm cream mixture.
Cook the custard over simmering water until thick enough to coat a spoon.
Strain berries and push through a sieve to create a purée, adding reserved liquid if needed.
Reserve a small amount of purée and custard for decoration and mix the rest.
Churn the berry custard in an ice cream maker according to instructions.
Preheat the oven to 200°C.
Simmer chopped apples with water for 4 minutes until soft.
Whisk apples into a smooth purée and let it cool.
Roll pastry to 30cm and score a margin 1cm from the edge.
Brush the pastry twice with beaten egg yolk.
Spread apple purée over the pastry, layer with sliced apples, brush with butter, and sprinkle sugar.
Bake for 30 minutes until golden and caramelised.
Slice the tart and serve with a scoop of berry ice cream.