Preheat your oven to 350°F (175°C) and line a 9x13 inch pan with parchment paper.

In a large mixing bowl, whisk together all-purpose flour, brown sugar, granulated sugar, baking powder, ground cinnamon, ground nutmeg, and salt.

Cut in the cold butter until the mixture resembles coarse crumbs, then stir in the beaten egg until just combined.

Press half of the crumb mixture into the prepared pan to form an even base and bake for 15 minutes.

In a separate bowl, mix chopped peaches, granulated sugar, cornstarch, lemon juice, and ground cinnamon until peaches are well-coated.

Spoon the peach mixture onto the pre-baked crust evenly.

Sprinkle the remaining crumb mixture over the peach layer.

Bake for an additional 40 to 50 minutes, until the top is golden brown and peach filling is bubbling.

Allow the bars to cool completely on a wire rack before slicing.