Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.

In a large mixing bowl, combine all-purpose flour, granulated sugar, baking powder, and salt. Cut in the unsalted butter until the mixture resembles coarse crumbs. Stir in the egg until fully incorporated.

Press half of the crumb mixture firmly into the bottom of the prepared baking dish.

In another bowl, combine the fresh peaches, brown sugar, cornstarch, ground cinnamon, and nutmeg. Stir gently until the peaches are well coated.

Carefully pour the peach mixture evenly over the crust in the baking dish.

Sprinkle the remaining crumb mixture generously over the peach layer.

Place the baking dish in the oven and bake for 45-50 minutes, or until the top is golden brown.

Remove from the oven and allow the bars to cool completely in the pan on a wire rack.