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 mixing bowl, cream together the softened butter and sugar until light and fluffy. Add the flour and salt, then mix 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 the diced peaches, 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. Add the cold cubed butter and cut it in 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, then sprinkle the streusel topping evenly across the surface.
07 - Return to the oven and bake for an additional 30 minutes, or until the streusel is golden brown and the filling is bubbling.
08 - Allow the bars to cool completely in the pan. Lift out using the parchment overhang, slice into 12 bars, and serve.