Makes 500ml

125ml whipping cream
1 vanilla pod
1 cinnamon stick
2 egg yolks 100g caster sugar
125g sour cream
175g good-quality apple puree or sauce

For the crumble
125g flour
90g unsalted butter
60g demerara sugar
60g nibbed almonds, optional

Pour the cream into a saucepan.
Split the vanilla pod and scrape the seeds into the cream.
Add the cinnamon stick and bring to the boil.
Whisk the egg yolks and sugar in a bowl.
Pour the cream over and stir until blended.
Return to the heat and cook gently, stirring continuously, until the custard coats the back of the spoon.
Remove from the heat, pass through a sieve and allow to cool, then stir in the sour cream and apple puree.
Now churn.

The crumble:
Preheat the oven to 180C/350F/Gas4.
In a bowl, rub together the flour, butter and sugar - and almonds if using - into a crumb.
Turn the mixture out into a baking tray and bake for 20 minutes, or until golden, stirring occasionally.
Remove from the oven and allow to cool.
Either sprinkle the crumble, warm or cold, on top of the ice cream, or add it two minutes before you finish churning.

This is versatile hot or cold.
Try any fruit puree or sauce.
Test using Greek yoghurt with lemon instead of sour cream. See how crumble freezes.