Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, cornstarch, baking powder, and salt.

In a large mixing bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy.

Add the egg and vanilla extract to the butter mixture and mix until smooth.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Gently fold in the chopped peaches and white chocolate chips.

Scoop the dough onto the prepared baking sheet, spacing about 2 inches apart.

Bake for 10-12 minutes or until edges are golden and centers are slightly glossy.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.