Peel and slice the apples using a mandolin. The slices should be 1mm / 0.03in thick. Start on one side until just before you reach the seeds. Then rotate the apple to slice the other side and so on. Only slice half the apples at first and then slice more as you need them to fill the mould. You don't want to be left with extra sliced apples.
Mix the sugar, salt and cornstarch.
Start by placing the apples on the base and make them come up the sides as well. You can see the video lines above for further reference.
In between each layer of apples, sprinkle the mix of sugar, cornstarch and salt. Repeat this until your mould is full.
Every 4 layers press down on the apples with your hands so they are nice and tight.
Cook in a preheated oven at 180°C / 350°F for 1 hour. Make sure to place the mould on a baking sheet because it tends to drip a bit and if it falls on the base of your oven, it will burn and smoke.
Remove it from the oven and unmould when it's warm. First, separate the apples from the sides with a knife os thin spatula. Place the dish you'll be serving it in on top and flip it.