1. Preparing the Brownie Batter

1. Preheat the oven to 350°F (175°C). Grease a 9×9-inch baking pan or line it with parchment paper.
2. In a bowl, combine the melted butter and granulated sugar. Add the eggs and vanilla extract, and mix until smooth.
3. Sift the flour, cocoa powder, and salt together, then fold them into the wet ingredients.
4. Gently fold in the blueberries, ensuring minimal stirring to maintain the fudgy texture.

2. Baking the Brownies

1. Pour the batter into the prepared pan and spread it out evenly.
2. Bake for 30-35 minutes, or until a toothpick comes out clean or with a few moist crumbs.
3. Let the brownies cool completely in the pan before adding the glaze.

3. Making the Blueberry Glaze

1. In a saucepan, cook the blueberries, sugar, and water over medium heat until the berries soften and the mixture becomes syrupy (about 10 minutes).
2. Strain the mixture to remove the solids, then whisk in the powdered sugar and lemon juice (if using) until smooth and glossy.

4. Assembling the Dessert

1. Drizzle the cooled glaze over the brownies, spreading it evenly to cover the surface.
2. Allow the glaze to set slightly before slicing the brownies into squares.