Put flour and sugar in a bowl, using your hand to mix.
Stir in melted butter, blend with fingers until the mix looks like crumble.
Spread onto a parchment-lined baking sheet, place into the oven for 15 to 18 minutes, or until the desired level of brownness. Remove from the oven and set crumble aside to cool.
Cook the apple filling:
Over medium heat, place apples and butter into the skillet. Once the butter has melted, add sugar, water, and spices, mix well.
Cook for 10 minutes or until apples are at the desired consistency.
Add flour and stir well, cooking for 2 more minutes. Remove from heat
Cook the Custard:
Mix flour, sugar, salt, and yolks in a bowl for a double boiler, mix well. Add milk and heavy cream.
Put on the boiler over medium heat, stirring frequently until thickened, about 12 minutes.
Remove from the boiler, set aside to cool.
Pour apple filling into a serving dish or divide between dessert coups, then layer with crumble, finally top with custard. Refrigerate until serving or serve immediately. Garnish with optional toppings, such as dried flowers, slivered almonds, or melting candies.
There will be leftover crumble topping which can be reserved for another use!