Preheat oven to 180C/350.

Grease a 20cm/8" square pan and line with baking/parchment paper with overhang (so it can be lifted out once cooked).

Mix together butter, flour, sugar, baking powder and salt until you can no longer see white bits of flour.

Add egg and mix.

Lightly press 2/3 of the mixture into the bottom of the pan.

Bake for 15 minutes until slightly golden, then remove and cool for 5 minutes.

Apple Filling: While the base is cooking, mix together Apple Filling ingredients in a bowl.

Add oats into reserved crumble mixture. Mix with wooden spoon / fingers until oats are mostly incorporated into the dough.

Spread Apple Filling on base, then use hands to crumble topping all over.

Bake for 30 - 35 minutes or until the top is deep golden.

Remove and allow to cool in the tin before lifting out of the tin using the baking paper.

Cut and serve! Eat with hands, or serve on plates. Take it over the top with ice cream and salted caramel sauce!