01 - Preheat oven to 350°F. Line a 9x13 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a large bowl, cream together the softened butter and sugar until light and fluffy. Add the flour and salt, mixing until the dough just comes together. Press the mixture evenly into the bottom of the prepared pan.
03 - Bake the crust for 15 minutes until lightly golden around the edges. Remove from the oven and set aside.
04 - In a medium bowl, combine the diced peaches, sugar, cornstarch, lemon juice, and vanilla extract. Stir gently until the peaches are evenly coated. Set aside to macerate while preparing the streusel.
05 - In a separate bowl, combine the flour, brown sugar, cinnamon, and salt. Pour in the melted butter and mix with a fork until the mixture becomes crumbly and resembles coarse crumbs.
06 - Spread the peach filling evenly over the pre-baked crust. Sprinkle the cinnamon streusel topping uniformly over the peach layer.
07 - Bake for 25 minutes, or until the streusel is golden brown and the peach filling is bubbling around 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.