01 - Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper and lightly grease.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well blended.
03 - In a large bowl, stir melted butter and brown sugar until smooth. Whisk in the egg and vanilla extract until fully incorporated.
04 - Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
05 - Gently fold in the blueberries and white chocolate chips if using, being careful not to crush the berries.
06 - Spread the batter evenly in the prepared pan. Bake for 28–32 minutes, or until the edges are golden and a toothpick inserted into the center comes out with a few moist crumbs.
07 - Cool completely in the pan before lifting out and cutting into bars.