Preheat oven to 350.
Grease a 9x9 pan with cooking spray and line with foil, leaving some foil to hang off the sides so you can lift out the bars. Set aside.
Sift together the flour and salt, set aside.
In a large mixing bowl cream the butter with an electric mixer, then gradually add in the powdered sugar.
Beat until smooth.
Slowly add in the flour mixture. I use a large serving spoon and add in the flour spoon by spoon. Mix until incorporated.
Spoon the dough into the prepared pan and press in the dough.
Bake for 25 minutes.
Take out the pan and let completely cool.
In the meantime prepare the caramel topping.
Place the sliced apples and peanuts in a bowl, pour in the freshly squeezed lemon juice, toss and set aside.
Put the caramels and butter in a soup pot and melt, stirring frequently.
As soon as the caramel has melted, remove from heat and stir in the apple mixture. Let cool for 5 minutes.
Pour the caramel mixture over the shortbread crust and put in the fridge until caramel sets and the crust hardens. About 2 to 4 hours.
Slowly remove the crust from the pan by holding onto the foil handles.
Cut into bars and serve.