Preheat your oven to 350°F (180°C) and prepare a 9x13-inch pan by greasing it or lining it with parchment paper.

In a food processor, combine all-purpose flour, granulated sugar, and salt. Pulse until mixed, then add cold unsalted butter, mixing until the texture resembles coarse crumbs. Press 2 cups of this mixture into the prepared pan, and bake for 15 minutes.

In a mixing bowl, combine the remaining crumb mixture with dark brown sugar. Use your fingers to work the mixture until large clumps form.

In a separate bowl, mix sugar, flour, ground cinnamon, and salt. Add your prepared peaches and gently stir to combine. In another bowl, whisk the heavy cream until smooth and fold it into the peach mixture.

Pour the peach filling evenly over the warm crust and sprinkle the streusel topping over the creamy layer.

Bake for approximately 45 minutes, until the filling bubbles and the topping turns golden brown.

Remove from the oven and let cool completely on a wire rack, preferably refrigerating for at least 2 hours before slicing.