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 evenly distributed.
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. Be careful not to 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, using a spatula to smooth the surface.
07 - 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.
08 - Cool completely in the pan before lifting out and cutting into bars. Store in an airtight container.