If you plan to make custard then take the milk out of the fridge and allow it to warm to room temperature in advance.
Slice the apple into 6-8 equal pieces and remove the core. Then cut the pieces into 5 mm thick wedges. It doesn't matter if you don't peel them.
Coat the apples in sugar and cinnamon powder and pack them into the bottom of a heat-resistant dish (I used light brown sugar).
Place the flour and butter into a plastic bag and rub together with your fingers until it becomes like fine panko (don't worry if a few lumps remain).
Mix the sugar into the mixture from Step 4 (this amount of sugar will make the crumble quite sweet so you can reduce it if you wish).
Lay the crumble over the apples from Step 3, and press it down with the palms of your hands to even out the surface.
Bake in an oven preheated to 180°C until the surface is golden. This should take approximately 40 minutes.
[Custard] Combine the eggs, sugar and 2 tablespoons of milk in a small saucepan and stir until smooth.
Warm the remaining milk in a microwave for 40 seconds without letting it boil. Then pour it into the saucepan a little at a time.
Place the saucepan over medium heat and continue to stir, without letting the mixture boil, until it thickens. When thick, stop the heat and add a dash of rum to finish.
Serve a portion of crumble in a dish with some hot custard.
Story Behind this Recipe
Apple crumble is usually made alongside dinner as a dessert rather than a stand alone snack. When I did a homestay in Britain I learnt how different British cooking is to Japanese cooking. I thought the simplicity of British cooking was wonderful and had my homestay family teach me this recipe.
Crumble is very sweet so it's fine if your apples are sour If the apples you are using are sweet then squeeze some lemon juice over them in Step 3. You can make the crumble in a plastic bag rather than a bowl. British people usually eat apple crumble with some hot custard, but it tastes delicious with ice cream too.