Step 1: Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone mats.
Step 2: Dice the fresh peaches into small, approximately 1/4-inch cubes. Spread them out on a few layers of paper towels and gently blot them dry to remove as much surface moisture as possible. This step is crucial for preventing soggy cookies!
Step 3: In a large mixing bowl, using an electric mixer, cream together the softened butter, granulated sugar, and brown sugar on medium speed until the mixture is light, fluffy, and pale in color, about 2-3 minutes.
Step 4: Beat in the egg and vanilla extract until well combined, scraping down the sides of the bowl as needed.
Step 5: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add these dry ingredients to the wet mixture, mixing on low speed until just combined. Be careful not to overmix.
Step 6: Gently fold in the diced, blotted peaches and white chocolate chips (if using) by hand with a rubber spatula. Mix only until evenly distributed, being careful not to crush the delicate fruit.
Step 7: Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between each cookie to allow for spreading.
Step 8: Bake for 10-12 minutes, or until the edges are lightly golden brown and the centers still look slightly soft. Do not overbake for that perfect chewy texture.
Step 9: Allow the cookies to cool on the baking sheets for 5 minutes before carefully transferring them to a wire rack to cool completely.