Preheat your oven to 350°F (180°C) and grease a 9x13-inch baking pan with butter or line with parchment paper.

In a food processor, combine all-purpose flour, granulated sugar, and salt. Add cubed cold unsalted butter and pulse until crumbly. Reserve 1½ cups for topping, then press remaining into the pan.

While the crust bakes, stir brown sugar into the reserved crumb mixture until clumps form, creating a streusel topping.

In a large bowl, mix granulated sugar, flour, cinnamon, and salt. Fold in peaches, then whisk together heavy cream and vanilla, folding into peach mixture.

Pour the peach filling over the baked crust, spread it evenly, then sprinkle the streusel topping over the peach layer. Bake for 45 minutes or until bubbly and golden.

Let the bars cool on a wire rack, then refrigerate for at least 2 hours before cutting.