Preheat your oven to 350°F (175°C). Lightly spray a 9x13 inch baking pan with non-stick cooking spray.

In a mixing bowl, combine the sugar cookie mix, softened butter, flour, and one egg to form a crumbly dough. Press the dough into the prepared pan to form a crust.

Evenly distribute diced peaches over the baked sugar cookie crust, pressing slightly into the crust.

In a separate bowl, whisk the eggs, sugar, cream, flour, and salt until smooth. Pour over the peaches.

Bake for 50 to 60 minutes until the custard is set and golden around the edges. Allow to cool before slicing.

Once cooled, remove from the oven and chill in the refrigerator for up to three days. Serve warm or chilled.