Blend blueberries in a food processor until smooth. Simmer the puree in a saucepan over medium heat until reduced to about 1/2 cup for 10-15 minutes. Cool completely.

Preheat your oven to 325°F (160°C) and line an 8x8-inch baking dish with parchment paper.

In a mixing bowl, whisk together melted butter and sugar until creamy. Add eggs one at a time, whisking well after each, then stir in vanilla and salt until smooth.

Fold the cooled blueberry reduction into the wet mixture, then gradually add sifted flour until just combined.

Pour the batter into the prepared baking dish and bake for 35-40 minutes. Check for doneness with a toothpick.

While cooling, whisk together powdered sugar, milk, and vanilla for the glaze until smooth.

Spread half of the glaze over the cooled brownies, let it set for 10 minutes, then add the remaining glaze. Slice into squares.