Remember to work with all the ingredients at room temperature for easy baking.
Press the shortbread base layer down really firmly. This gives you a good firm base for the filling that will not fall apart when cut.
There is no need to bake the base before the filling and topping. Since we are adding cornflour to the apples, any liquid that comes off the fruit will thicken up and become more of a sauce, so you will not get a soggy bottom.
If you wish to add the caramel in with the apples instead, simply drizzle the tops of the apples generously with caramel before topping with the remaining shortbread mixture. Bake as before, but keep in mind this may also result in a little caramel bubbling through the top of the bake,
Leave the bars to cool completely before cutting. If you cut too soon, the middle will still be warm and so the whole thing will fall apart as you cut it. It will be worth the wait!