Start by whisking together cornstarch, sugar, and salt in a mixing bowl. Add the egg yolks and beat until the mixture lightens in color. Set aside.

In a pot over medium heat, combine milk and vanilla extract (add vanilla bean if using). Heat until it just starts to bubble at the edges—be careful not to boil.

Remove from heat and gradually add the warm milk to the egg mixture, whisking continuously to prevent the eggs from cooking.

Transfer the mixture back to the pot and heat over medium-low, whisking constantly until it thickens. Remove from heat and stir in the butter until melted and smooth. Transfer the custard to a bowl.

Preheat your oven to 325°F.

In a small bowl, mix together melted butter, white sugar, flour, oats, and salt until it forms a dough.

Spread the dough onto a parchment-lined baking sheet and bake for 10-12 minutes until golden. Let it cool.

In a pan over medium heat, combine butter, apples, brown sugar, cinnamon, salt, vanilla extract, and lemon juice. Simmer for 6-8 minutes until the apples are soft.

In a small bowl, mix water and cornstarch to create a slurry. Add it to the pan to thicken the filling, then remove from heat.

In a large cup or bowl, layer the apple pie mix, followed by the shortbread crumble, and top it all off with the hot custard. Enjoy the cozy goodness!