Put the flour and brown sugar into a large mixing bowl. And add the cubed butter and use your fingers to lightly rub the ingredients together until it resembles breadcrumbs.
Drizzle over 2 tablespoons of water and use a fork to roughly mix it through so there are some clumps. Add the almond flakes and oats and stir through until just mixed. Put the mixture into the fridge while you prepare the filling.
Prepare the fruit. Preheat the oven to 200C/180C fan.
Soak the currants in 50 millilitres brandy and 50 millilitres boiling water. Leave to stand while you prepare the apples.
Butter a large oven dish. Peel and core the apples - you can use any type but Bramley (cooking) apples hold their shape well during cooking. If you use regular apples, you don’t need to stew them first. Chop the apples into 2 centimetres or so chunks, and put them into a large bowl of iced lemon water as you go, so that they Iced lemon water to stop the fruit discolouring.
Drain the apples and add them to a large, wide saucepan 2 tablespoons of water. Cook the apples on a low heat for about 5 minutes, stirring occasionally until they just start to soften, then turn off the heat. Mix the caster sugar and cinnamon together then add that to the pan along with the drained currants.
Gently mix the cinnamon sugar and currants through the apples. Tip the fruit into the buttered oven dish, then spoon the chilled crumble topping evenly over the top.
Bake in the preheated oven for 30-35 minutes until the fruit is cooked and the topping is golden brown and crisp. Turn around halfway through cooking if it’s colouring unevenly.
Use a knife or skewer to check the apples are cooked then leave to stand for 15 minutes before serving.
Make the custard while the crumble is cooking
Put the milk and vanilla seeds into a saucepan and bring to a gentle simmer, then switch off the heat.
In a large mixing bowl, whisk together the sugar, cornflour and egg yolks.
Pour the hot milk onto the egg mixture while whisking the eggs so lumps don’t form. Once smooth, return to the saucepan and cook on a low heat, stirring with the whisk constantly. It will take a few minutes for the sauce the thicken up. Don’t let it come to a boil.
Once thickened, pour into a warmed serving jug. Cover the top of the custard with clingfilm to keep the heat in and stop a skin forming.