Split the vanilla pod lengthwise and scrape out the seeds.

Heat the whole milk with the vanilla pod and seeds until steaming.

Remove the milk from the heat and infuse it for 60 min if time allows.

Whisk the egg yolk with 22 g granulated sugar until fully combined.

Gradually whisk the hot vanilla milk into the egg-yolk mixture.

Return the custard mixture to the saucepan and cook over low heat.

Stir and scrape the bottom until the custard thickens and coats a spoon.

Strain the custard through a fine sieve into a bowl.

Cover the custard and chill it in the refrigerator.

Peel, core, and dice 250 g green apple.

Combine the diced apple, 22 g brown sugar, vanilla extract, and 1/2 tsp cinnamon in a saucepan.

Cook the apple mixture over medium heat and stir gently until its juices evaporate.

Remove the caramelised apple base from the heat and allow it to cool.

Rub 29 g butter into 36 g flour until the mixture resembles cornmeal.

Stir 16 g brown sugar, 7 g granulated sugar, walnuts, and 1/3 tsp cinnamon into the crumble.

Refrigerate the crumble mixture for 30 min to firm it.

Preheat the oven to 150°C / 302°F.

Spread the cooled apple base evenly in the ovenproof baking dish.

Scatter the chilled crumble evenly over the apple base.

Bake the crumble at 150°C / 302°F for 30 min until the topping is crisp.

Divide the warm crumble between 2 servings and add one scoop of vanilla ice cream to each.

Spoon the chilled vanilla custard around or over each serving.