Blend 1 cup of blueberries in a blender until smooth to make blueberry puree.

Cook the blueberry puree in a saucepan over medium-low heat for about 8-10 minutes until reduced to ½ cup.

Preheat oven to 325°F (163°C) and prepare an 8x8-inch baking dish by lining with parchment paper.

In a mixing bowl, combine melted butter and granulated sugar, then add eggs, vanilla extract, and salt, whisk until smooth.

Fold in the cooled blueberry puree into the wet mixture.

Sift in all-purpose flour and fold gently until combined.

Spread the brownie batter evenly in the prepared baking dish and bake for 35-40 minutes.

Let brownies cool in the dish for about 20 minutes, then cool completely on a wire rack before glazing.

Whisk together powdered sugar, milk, and vanilla extract until smooth for the glaze.

Spread the glaze over the cooled brownies and let it set for about 15 minutes.

Cut the brownies into squares and store in an airtight container.