Preheat your oven to 350°F (175°C) and grease a square baker.

In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined.

Add the eggs and vanilla extract to the sugar mixture, and whisk until smooth.

In a separate mixing bowl, sift together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Stir in the lemon zest and lemon juice until evenly incorporated into the batter.

Gently fold in the blueberries, being careful not to overmix.

Pour the batter into the prepared baking dish and spread it out evenly with a spatula.

Bake in the preheated oven for 25-30 minutes, or until the blondies are lightly golden brown around the edges and a toothpick inserted into the center comes out clean.

Remove the blondies from the oven and allow them to cool completely in the pan before slicing and serving. Enjoy these Lemon Blueberry Blondies as a deliciously citrusy dessert, perfect for any occasion!

If desired, mix 6-8 tablespoons of powdered sugar with the juice of a lemon in a small mixing bowl to create an icing to drizzle on top.