01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Add the flour and salt, mixing until a crumbly dough forms.
03 - Press the dough evenly into the bottom of the prepared pan. Bake for 15 minutes until lightly golden around the edges.
04 - While the crust bakes, combine the diced peaches, granulated sugar, cornstarch, and lemon juice in a bowl. Toss gently until the peaches are evenly coated.
05 - In a separate bowl, combine the flour, brown sugar, cinnamon, and salt. Cut in the cold cubed butter using a pastry cutter or your fingers until large, pea-sized crumbs form.
06 - Remove the par-baked crust from the oven. Spread the peach filling evenly over the hot crust. Sprinkle the streusel topping uniformly over the peach layer. Bake for an additional 30 minutes until the streusel is golden brown and the filling is bubbling.
07 - Allow the bars to cool completely in the pan. Lift the entire slab out using the parchment overhang. Slice into 12 even bars and serve.