Preheat the oven to 350 degrees F. Lightly grease an 8x8-inch pan with cooking spray, line with parchment paper (so that you have some overhanging two sides), then lightly grease again. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl, beat the butter and sugar at medium speed until light and creamy, about 2 minutes.
Add the eggs one at a time, beating between each addition, then beat in the vanilla extract.
Sprinkle the baking powder and salt over the top, then mix to combine. Reduce the mixer speed to low and, with the mixer running, slowly add in the flour, mixing just until it disappears. Stop to scrape down the bowl as needed to make sure the ingredients are evenly blended. The dough will be very moist and sticky.
Reserve 1/2 cup of the dough for the topping, then scrape the remaining dough into the bottom of the prepared dish. With a knife, the back of a spoon, or an offset spatula, spread the dough into an even layer, smoothing it all the way into the corners. The layer will seem thin, but it will rise and thicken as it bakes.
Mix the sliced almonds into the reserved dough, and mix to combine. Set aside.
Spoon prepared pie filling (make sure it's cool) over the top of the bottom layer. Spread it into an even layer, then drop small spoonfuls of the reserved dough with almonds over the top of the bars. Some of the cherry pie fillingwill show through.
Bake for 50 to 55 minutes, until lightly golden on top and set. Place the pan on a wire rack and let cool completely. To remove the bars from the pan, use a dull knife to loosen the sides, then gently lift them out using the overhanging parchment paper.
To make the glaze, whisk together the powdered sugar, almond extract, and milk until smooth. Drizzle over the bars, slice, and serve.
Notes
TO STORE: Store leftover cherry bars in the refrigerator for up to 4 days.
TO FREEZE: Wrap individually in plastic and freeze for up to 2 months. Let thaw overnight in the refrigerator.
TO REHEAT: You can enjoy these cherry bars straight from the fridge. However, they're also tasty warmed in the microwave for 10-15 seconds too.