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, beat softened butter and sugar together until light and fluffy. Add 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.
04 - While the crust bakes, combine diced peaches, sugar, cornstarch, and lemon juice in a bowl. Toss gently until peaches are evenly coated.
05 - In a separate bowl, combine flour, brown sugar, cinnamon, and salt. Cut in cold butter using a pastry cutter or your fingers until large crumbs form.
06 - Remove the crust from the oven. Spread the peach filling evenly over the hot crust. Sprinkle the streusel topping evenly over the peaches. Bake for an additional 30 minutes until the streusel is golden and the filling is bubbling.
07 - Allow the bars to cool completely in the pan. Lift out using the parchment overhang, then slice into 12 bars and serve.