01 - Preheat 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.
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.
06 - Spread the batter evenly in the prepared pan using a spatula.
07 - Bake for 28-32 minutes, until edges are golden and a toothpick inserted into the center comes out with a few moist crumbs.
08 - Cool completely in the pan before lifting out and cutting into bars.