01 - Preheat the oven to 350°F. Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a large bowl, cream the softened butter and granulated sugar together until light and fluffy. Add the flour and salt, then mix until the dough just comes together.
03 - Press the dough evenly into the bottom of the prepared pan. Bake for 15 minutes until the edges are lightly golden. Remove from the oven and set aside.
04 - In a medium bowl, toss the diced peaches with granulated sugar, cornstarch, lemon juice, and vanilla extract until evenly coated. Set aside to macerate.
05 - In a separate bowl, combine the flour, packed brown sugar, cinnamon, and salt. Pour in the melted butter and mix with a fork until the mixture forms coarse, crumbly clusters.
06 - Spread the peach filling in an even layer over the pre-baked crust. Sprinkle the cinnamon streusel evenly across the top.
07 - Bake for 25 minutes, or until the streusel topping is golden brown and the peach filling is bubbling at the edges.
08 - Allow the bars to cool completely in the pan. Use the parchment overhang to lift the slab out, then cut into 12 even squares.