My crumble rules:
1. Custard with crumble fresh from the oven, cream when it’s cold. The latter good on a cycle ride.
2. Demerara a very good choice for the crumble mix.
3. Never put cinnamon in an apple crumble.
4. Overripe banana: mash & mix 50:50 with plain yogurt and a little sugar, yum-yum.