The filling should be prepared first so that it can cool to room temperature. Coling can take a couple of hours.
Bring to a very gentle boil, stirring constantly at all times. You have to stay with this caramel at all times and NOT stop stirring it or it will definitely stick to the bottom and burn. I find a wooden spoon is best for this and if you have one of those straight bottom paddle types that can scrape the bottom of the pot continuously as you stir, definitely use that. What you are trying to do here is develop a little colour in the caramel, not too much or your caramel will go hard. It will pick up a bit more colour in the oven so just a light golden colour is fine. This process should take about 10-15 minutes .
It is very important to cool the filling to room temperature before proceeding. A hot filling will immediately melt the butter in the shortbread and ruin the cookies.
To prepare the Shortbread Crumble
Press about 1/2 of the crumble firmly into the bottom of the pan. I generally refrigerate the pan plus the remaining crumble for the top until the filling cools completely. Cold shortbread dough always bakes better.
Spread the cooled filling evenly over the bottom layer of shortbread in the pan.
Press the remaining crumble together in handfuls and break off little pieces about the size of the top of your pinkie finger. Scatter these evenly over the caramel layer.
Bake for 30 minutes until the top is a nice golden brown.
The nutritional information provided is automatically calculated by third party software and is meant as a guideline only. Exact accuracy is not guaranteed. For recipes where all ingredients may not be used entirely, such as those with coatings on meats, or with sauces or dressings for example, calorie & nutritional values per serving will likely be somewhat lower than indicated.