Preheat the oven to 350°F (175°C). Line a 9×13 inch baking dish with parchment paper.
In a medium bowl, combine the flour, granulated sugar, softened butter, and salt. Mix until the mixture becomes crumbly. Press this mixture firmly into the bottom of the prepared baking dish to form the crust.
In another bowl, gently toss the peach slices with the brown sugar, cornstarch, ground cinnamon, and vanilla extract until the peaches are evenly coated. Spread the peach mixture over the crust in the baking dish.
Bake in the preheated oven for 40-45 minutes, until the crust is golden brown and the peach mixture is bubbling.
While the bars are baking, prepare the glaze by whisking together the powdered sugar, milk, and lemon juice in a small bowl until smooth.
Once the bars have finished baking, allow them to cool completely in the baking dish. Drizzle the glaze over the cooled bars.
Cut into squares and serve, enjoying the burst of fresh summer flavors in every bite.
