Weigh or measure the white and light brown sugars and add them to the bowl of a food processor. Next, weigh or measure the flour. Add to the flour, the cinnamon and the salt. Run a whisk through to blend. Add the flour mixture right on top of the sugars. Finally, add the cubed cold butter right on top of the sugar-flour mixture in the food processor bowl.
I do a couple of 5 second pulses, then continue with 10 - 12 quick pulses. You want the shortbread to be coming together with medium to small balls of dough. Depending on your food processor, you may need a few more pulses. Then move the dough to a dish.
Butter and flour a 9 X 9 square baking pan. Take a sheet of parchment paper and cut the length so it lines the bottom and up and over 2 opposite sides. These will be handles (check photo in the post for example). Take half of the shortbread dough that you got from the food processor and spread it around the bottom of the baking pan, right on top of the parchment paper. Press down on the dough so that you have the whole bottom of the pan covered. Take the Old Fashion Oats, and spread it on top of the shortbread dough. Press down lightly so they won't move much when baked.
Preheat the oven to 350°F (175°C or 180°C). Bake for 13-15 minutes. You want a light-colored bake. It will be a little soft, but that is perfect; it will be baked again. Let it cool for 10 minutes or until you can handle the pan with your hands.
Grab the raspberry filling and you want to spread half on top of the partially baked shortbread. Then take the white chocolate chips and sprinkle them on top of the filling. Now take the other half of the raspberry filling and cover the white chocolate chips. Take the remaining half of the shortbread pieces and drop them around on top of the raspberry filling. If some pieces are too big, break them up into smaller pieces. Finally, take the almond slices and sprinkle them on top of the shortbread pieces. Ready for the oven.
Bake at 350°F (175°C or 180°C) for 35 to 40 minutes. Once out of the oven, let it cool on a cookie rack for an hour. Afterwards I like to chill the shortbread for about 20 minutes just to firm everything up before cutting it into bars. Don't leave it in the fridge long shortbread seems to collect moisture from the fridge and will get soft.
You can slide the shortbread out by tilting the pan and pulling on one of the parchment paper handle or cut it right in the pan. I put them in a container, but don't put the lid on tight. I keep the lid off or just lay the lid across the top. If the bottom gets soft and moist, I line the bottom of the container with a paper towel sheet.