1. Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving some overhang to make lifting the bars easier later.
2. In a large bowl, whisk together the flour, sugar, baking powder, and salt. I never measure too precisely—Mama Lu always said, “A pinch more or less won’t hurt.”
3. Add the cold butter cubes to the dry ingredients. Using your fingers or a pastry cutter, work the butter into the flour mixture until it resembles coarse crumbs. This step is like kneading biscuit dough with your hands—warm hands, quick work.
4. In a small bowl, beat the egg and vanilla extract together, then stir into the crumb mixture. The dough will be crumbly but should hold together when pressed.
5. Press about two-thirds of the dough evenly into the prepared pan to form the base. Pat it down firmly, like pressing down on a fresh biscuit dough in the skillet.
6. In another bowl, toss the chopped cherries with cornstarch and, if using, the cherry jam. This keeps the filling from becoming too watery while locking in that bright cherry flavor.
7. Spread the cherry mixture evenly over the dough base, leaving a small border around the edges.
8. Crumble the remaining dough over the cherry layer, covering as much as you can without pressing it down too hard.
9. Bake in the preheated oven for 35-40 minutes, or until the topping is golden brown and the cherry filling bubbles up through the cracks.
10. Once out of the oven, let the bars cool completely in the pan on a wire rack. When cool, lift the bars out using the parchment overhang and cut into squares.
11. If you like, dust with powdered sugar before serving, but don’t be surprised if they disappear before you get to that step.

Over the years, I’ve learned that patience is key here—letting the bars cool fully helps the filling set and makes slicing easier. Mama Lu used to say, “Good things come to those who wait—and those who have a cold glass of buttermilk handy.”