Put the apples, lemon juice, cinnamon stick and sugar in a deep pan, cover and cook over a gentle heat for 8 to 10 minutes until the apples begin to soften.
Put the flour, ground almonds and butter into a food processor and whizz until they form breadcrumbs. Stir through the oats and ground cinnamon.
Heat oven to 200°C, 180°C fan. Remove the cinnamon stick from the apple mixture, pour the mix into the baking dish, top with the crumble, dot with extra butter, and poke the cinnamon stick into the centre. Bake for 40 to 45 minutes, until the topping is golden brown.
Take 600ml milk and 55ml pouring cream, and place in a saucepan with 1tsp vanilla extract. In a large bowl, mix together 4 egg yolks with 30g castor sugar and 2tsp cornflour.
Scald the milk, then pour onto the egg mixture, stirring well. Return to the pan and, over a gentle heat, keep whisking gently with a balloon whisk until the custard has thickened and has an almost jelly-like wobble.
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