Preheat your oven to 350 degrees F. and line a 9×9 baking dish with parchment paper. Make sure the edges of the paper hang over the edges of the pan so you can remove the bars easier.
In a large sized bowl, beat together the butter and sugar. Add the eggs and the vanilla and beat until very well combined.
Now add the flour and salt to your butter mixture and mix until combined.
Press the dough into the bottom of the parchment lined pan in an even layer as possible.
Spoon the apple pie filling over the top of the crust and gently spread to completely cover the crust.
Start the streusel topping by whisking together the brown sugar and flour in a medium size bowl.
Add in the cubed butter into the flour brown sugar mixture. Use a pastry blender or fork to combine until the mixture resembles coarse sand.
Evenly sprinkle the streusel topping over the pie filling. Place in your preheated oven and bake for 35 minutes.
The pie bars are finished baking when the filling is bubbling and the streusel topping is golden brown.
Allow the apple pie bars to cool completely, then remove them from the pan by pulling the edges of the parchment paper up. Cut into bars before serving.