Preheat the oven to 350 degrees F. Line a 9x13 pan with tin foil and spray with cooking spray.
In a large mixing bowl, use a hand mixer to beat butter and shortening until smooth and fluffy. Add sugar, baking powder and salt. Beat until combined, scraping the sides of the bowl occasionally.
Add eggs and vanilla and mix until well combined. Add 2 cups of flour and beat it into the dough. Add the last cup of flour. If it gets too thick, use a silicone spatula or wooden spoon to incorporate the rest of the flour in.
In a small bowl, reserve 1 1/2 cups of the dough. Spread the remaining dough into your prepared 9x13 pan.
Bake for 12 minutes. Using a spoon, scoop and gently spread the pie filling over the crust in the pan.
From your reserved dough, get a small handful and flatten it out to about 1/4" thick and place it on top of the pie filling. Repeat until all reserved dough has been used. There will be places where the pie filling can be seen so you don't need to try and cover it completely.
Bake for another 30 minutes, or until the top is light brown. Remove from the oven and cool on a wire rack for 10 minutes. While it's cooling, make the powdered sugar icing. (see below)
After 10 minutes of cooling, use a spoon to drizzle the icing over the top of the bars. Let cool completely before cutting into bars to serve.