> My mum has always cooked them first with cinnamon and sugar
I've always understood that you should cook fruit before adding the sugar otherwise it doesn't smash down properly ?? I never add sugar to the Bramleys as I feel that there is enough sugar in the crumble. I also never add sugar to custard if it is going to be eaten with something sweet :)
Last year I tried both ways and now cut the apples into wedges, sprinkle with sugar and cook from raw in the pie as I prefer them to still have a bit of shape when the crumble is cooked.