Preheat the oven to 350°F. Grease and flour an 8x8-inch baking pan or line it with parchment paper.

Whisk the melted butter and brown sugar in a mixing bowl until well combined. Add the egg and vanilla extract and continue to whisk until smooth. If you are using a stand mixer, use medium speed.

Sift the flour, baking powder, and salt in a separate bowl.

Gradually add the flour mixture to the wet ingredient mixture until just combined. Be careful not to overmix.

Gently fold the drained diced peaches and stir, ensuring they are evenly distributed throughout the batter.

Pour the batter into the prepared baking pan and spread it out evenly. Place the pan in the preheated oven and bake for 25-30 minutes, until the edges are golden brown and a toothpick inserted into the center comes clean.

Allow the peach blondies to cool in the pan for 10-15 minutes before slicing them into squares using a butter knife. Serve warm or at room temperature. Enjoy your delicious peach blondies!