Preheat your oven to 100°C (210°F). In a saucepan over medium heat, melt the granulated sugar without stirring, watching closely for it to turn golden brown. Pour the caramel into your prepared mould, letting it set slightly.

Peel and slice your chosen apples using a mandolin for consistent, 1mm thick slices. Start with half the apples and continue slicing as necessary.

Begin layering the apple slices in the mould. Sprinkle a mix of sugar, a pinch of salt, and cornstarch between the layers of apples. Press down every four layers.

Place the mould on a baking sheet and slide it into your preheated oven at 180°C (350°F). Let it bake for about 1 hour.

After baking, allow the mille-feuille to cool slightly before unmoulding. Run a knife around the edges to loosen it.

In a bowl, whisk egg yolks and cornstarch together. Heat milk, sugar, vanilla paste, and salt until steaming. Gradually whisk this into the egg yolks, then return to the pot. Stir continuously over low heat until thickened.