Apple Crumble Pie with Blueberries / Appelkruimeltaart met bosbessen

Similar to the crumble cake recipes I reviewed a while ago (I wrote this review, the rest were family recipes). What was different about this cake is that all the recipes back then used a one batter for the base and a another one for the crumble. This recipe tries to use a single batter for both... and fails. The base is very wet, and I can't tell if that is liquid from the blueberries or if the cake hasn't cooked through properly, while the crumble isn't crisp at all.

I had a look at the ratio of ingredients. Compared to other base batters (it's neither a pound nor a sponge nor a butter cake - in German you'd call all of these batters rather generically 'Rührteig', batter that is stirred), it contains very few eggs - other recipes contain up to 6 eggs for roughly the same amounts of flour, butter and sugar while this one uses only one. For the crumble, it just the other way around, none of my crumble recipes uses an egg, while this one does.

My guess is that the author tried to make this recipe easy, but sometimes, it's just worth it to walk the extra mile.