Preheat the oven to 350ºF (180ºC). Lightly grease a 9-inch (23-cm) square pan and line it with parchment paper. Set aside.
Place the flour, baking powder, and salt in a mixing bowl and whisk until well combined. Set aside.
In a second mixing bowl, whisk the melted butter, brown sugar, eggs, and vanilla extract until creamy and smooth.
Add the dry ingredients and white chocolate chips to the bowl of wet ingredients and fold them together halfway. Add the blueberries. Gently fold the batter together until the flour is just mixed in and the blueberries are well distributed. Spoon the batter into the prepared baking pan and gently smooth it into an even layer. Bake for 47 to 50 minutes, or until the blondies are golden and no longer look wet and shiny on top. Transfer to a wire rack to cool completely before slicing and serving.
Notes
Using an oven thermometer will give you the most accurate and consistent results.
Let your blueberry blondies cool completely in the pan on a wire rack before slicing to ensure they set properly and hold their shape.
Storage
Store in an Airtight Container: The blondies can be kept in an airtight container at room temperature for up to 3 days.
Refrigerate for Longer Storage: For longer storage, refrigerate for up to one week.
Freeze for Extended Storage: To freeze, place fully cooled blueberry blondies in a freezer-safe bag or container for up to 2 months. Thaw at room temperature before serving.