• Preheat oven to 350 F (180 C) for conventional oven, 330 F (165 C) for convection oven
• I use a 7-inch round cake pan. Line the bottom and side with parchment paper. If you use a loose-bottom pan, line the bottom with parchment paper. You can also use 8 1/2 x 4 1/2 or 9 x 5 inch loaf pan. Line the side and bottom of the pan with parchment overhanging so you can easily lift the cake up to unmold

Prepare the crumble topping:

• Combine flour, sugar, and cinnamon. Gradually drizzle in the melted butter while stirring the flour mixture with a fork at the same time. You don't want to overmix this mixture. It supposed to resemble crumbles, not a dough. There should be a mixture of different sizes of crumble. Cover and keep in the fridge while you prepare other things

Prepare the cake batter:

• Whisk flour, salt, ground cinnamon, ground nutmeg, and baking powder to combine and set aside
• In a large mixing bowl, combine room-temperature eggs with sugar and whisk until sugar dissolves. Add melted butter and whisk again until combined. Add the room-temperature milk and whisk again until combined. The eggs help to emulsify the mixture
• Sift in the flour mixture and use a whisk to combine. Set the cake batter aside
• Peel the apples and core. Then thinly slice the apples, about 2 mm in thickness. I got around 650-680 grams of apple slices (in case you want to know!). You can also use a mandoline slicer to make your life easier
• Add the apple slices into the cake batter and gently mix to make sure the apples are coated in the cake batter evenly
• Pour half of the cake batter gently into the prepared pan. Use a spatula to press the cake batter down evenly to ensure there won't be any "holes" inside the batter. If you are really obsessive about it, you can try to have the apples slices stacked up horizontally as neatly as possible. Then pour the rest of the cake batter into the pan and again, gently press with a spatula to make sure the apple slices are packed in without leaving any holes
• Sprinkle the crumble topping evenly on top of the cake batter

Bake the cake:

• Put the pan in the middle rack of the oven and bake for the next 55-60 minutes or until a cake tester inserted into the center of the cake, comes out clean with a few crumbs are okay, as long as it's not wet. If it's still wet, bake for another 5 minutes and check again. If the cake browns too quickly, loosely tent with an aluminum foil for the last 10 minutes of baking

Cool down:

• Let the cake cool down completely in the pan set on top of a cooling rack. Once it has cooled down completely, I highly recommend chilling it in the fridge. It allows the "custard" to set further. We like to serve it cold because it gives that dense texture in a good way. But, if you prefer to serve it without chilling it in the fridge, that's totally fine too

Storing:

• Store leftovers in an air-tight container in the fridge for up to 5 days. Do not freeze as the custard-like inner texture changes