Preheat your oven to 350°F (180°C). Prepare a 9×13-inch pan by greasing it or lining it with parchment paper, ensuring you leave some overhang for easy lifting after baking.

Make the crust: In a food processor, combine 2 1/2 cups flour, 2/3 cup granulated sugar, and 1/2 teaspoon salt, pulsing until mixed. Add the cold butter cubes and pulse again until it creates a crumbly texture. Reserve 1 1/2 cups of the crumb mixture for the topping and press the remaining crumbs firmly into the bottom of the prepared pan. Bake for approximately 15 minutes until the edges start to brown.

Prepare the streusel topping: In the reserved crumb mixture, mix in 1/4 cup brown sugar until clumps form.

Create the filling: In a large bowl, combine 1 cup granulated sugar, 1/4 cup flour, 1/2 teaspoon cinnamon, and 1/4 teaspoon salt. Toss in the chopped peaches until coated. In a separate bowl, whisk together heavy cream and optional vanilla extract, then add to the peach mixture.

Once the crust is done, pour the peach filling over the warm crust evenly. Top with the streusel mixture.

Return the pan to the oven and bake for about 45 minutes, or until the juices are bubbling and the topping is golden brown. Allow to cool completely on a wire rack.

For best flavor, refrigerate the bars for at least 2 hours before cutting into squares. They will keep covered in the refrigerator for up to 3 days.

To freeze, wrap bars tightly in plastic wrap and place in a freezer-safe container for up to 3 months.