Preheat the oven to 375°F. Line a 9x13” baking dish with parchment paper.
Make the Crust and Topping
Whisk the flour, sugar, and baking powder in a large bowl. Add the butter, egg, and vanilla. Use a fork or pastry cutter to cut the butter in until the mixture is crumbly.
Press half of the mixture into the prepared pan. Set the rest of the mixture aside.
Make the Filling and Bake
Mix the granulated sugar, brown sugar, and cornstarch in a large bowl. Add the peaches and toss them in the sugar mixture until they are evenly coated.
Place the peaches in an even layer over the crust in the pan. Crumble the topping over the top of the peaches.
Bake the peach bars for 40 to 45 minutes or until the crumble topping is golden brown.
Wait until the bars are at room temperature before slicing them. You won't get clean slices if you slice them when they are hot or warm. Once they are cool, use the parchment paper to lift them out of the pan and then slice and serve them.
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Notes
Lining the pan with parchment will make it easy to lift the bars out in one piece before you slice them. To make it easy to line the pan, spritz it with a few shots of cooking spray and then line it with the parchment. The spray will help hold the paper in place.You don't have to peel the peaches for this recipe. Give them a good wash, remove the pits, and chop them up.If prefer to remove the skin, you can peel the peaches first. Bring a large pot of water to a boil, drop the peaches in for about 30 seconds, and then transfer them to an ice bath. This will make it easy to remove the peels.You can make these bars ahead and store them at room temperature or in the refrigerator. At room temperature, they're best within a day or so. They'll keep for a few days longer in the refrigerator.