Preheat your oven to 350°F/175°C. Butter a 8x8 or 9x7 dish
Whisk together the flour, cinnamon, ginger,, salt, oats and brown sugar together in a large jug or medium bowl. Add in your cubed butter and use your fingers or a pastry cutter to rub the butter until it is very crumbly and everything is moistened. Place in the fridge while you prepare the filling.
In a large bowl, mix all of your filling ingredients together and toss. Make sure the apple slices are evenly coated.
Spread the apples out into an even layer of your dish. Make sure there are no gaps! Sprinkle over your topping mixture evenly
Bake for 50-55 minutes. If it gets too brown, place some foil on top
Allow it to cool for at least 5 minutes before serving
Custard
In a medium saucepan, add your vanilla extract, milk and heavy cream. Bring to a simmer at a medium-low heat - do not allow it to boil!
In a medium bowl, whisk together the egg yolks, cornstarch and sugar. Whisk until it is smooth.
Pour the hot milk mixture a cupful at a time into the egg yolks, whisking the yolks constantly - this ensures it doesn't scramble.
Turn the heat off, and quickly clean and dry your saucepan. Place the pan on low heat and pour in the mixture. Stir constantly with a wooden spoon until it is thick - this could take up to 20 minutes. It's ready when you can draw a line through the custard. Pour into a large jug and place plastic wrap on to the surface, this will stop a skin from forming.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven’t tested the recipe with this method. Just click on 'US Customary' above the ingredient list to find the cups. Butter: I use European style butter, like Kerry Gold, in my recipes. Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Storage: Keep the apple crumble covered and in the fridge for up to 5 days.