Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish or line it with parchment paper for easy removal.

In a large mixing bowl, combine the flour, granulated sugar, baking powder, and salt. Mix well.

Add the softened butter, egg, and vanilla extract to the dry ingredients. Use a pastry cutter or your hands to mix until the mixture resembles coarse crumbs.

Reserve 1 cup of the crumb mixture and press the remaining mixture evenly into the bottom of the prepared baking dish to form the crust.

In another bowl, toss the diced peaches with lemon juice, cinnamon, nutmeg, and brown sugar until well coated.

Spread the peach mixture evenly over the crust in the baking dish.

Crumble the reserved crumb mixture over the peaches to create a topping.

Bake in the preheated oven for 30-35 minutes, or until the top is golden brown and the peaches are bubbly.

Allow the bars to cool in the pan for at least 15 minutes before slicing into squares.