I use half oats and half flour for mine (same total amounts as AMIS; it makes it lovely and crunchy & tastes better too. I also use butter because I hate marge and soft brown sugar. I often add a little bit of cinnamon too. I often add some raspberries to the apples, because my dad grows them & is always giving me more from his freezer. My brother has just brought me some Peasegood apples from his tree, so I'm going to make one this weekend.
I like to use eating apples rather than bramleys. I cook the apples first with a bit of muscovado sugar and cinnamon. I don't press the crumble down and I use muscovado in that aswell. Then 25 mins in oven. Yummy. Custard in our house too. Even better with plums (drools) I think I'd better go and make some now byee