How do you make a smooth and creamy apple custard?
Bake the apples and have them dry and crisp up (cut the apples thin so that they dry up evenly and crisp faster) and concentrate the flavour. Then blend to a powder and mix into the custard.
Cook and reduce the apples till a very tender gooey apple pie texture comes and then thicken and reduce excess water as to not thin out the custard, mash till homogenized and fold in with custard.
Get something like apple juice and reduce till thick and add sugar to make syrup and use that in addition or in place (depending how much you want in) of the sugar for the custard recipe.


Personally I'd go with the first option though time consuming.