1. Blend the blueberries in a blender until completely smooth to make a puree.

2. Pour the blueberry puree into a saucepan over medium-low heat and gently simmer, stirring constantly, until reduced to about 1/2 cup.

3. Remove the reduction from heat and allow it to cool completely.

4. Preheat the oven to 325°F (163°C) and line an 8×8 inch glass baking dish with parchment paper.

5. In a medium bowl, combine the melted butter and granulated sugar.

6. Stir in the eggs, vanilla extract, and sea salt until the mixture is smooth and uniform in color.

7. Fold the cooled blueberry reduction into the wet mixture until incorporated.

8. Gradually add the sifted flour and stir until just combined.

9. Pour the batter into the prepared baking dish and spread evenly.

10. Bake on the middle rack for 35–40 minutes, checking at 30 minutes, until the center is set and a toothpick inserted comes out clean or with a few crumbs.

11. In a bowl, whisk together powdered sugar, milk, vanilla extract, and a pinch of salt until smooth to make the glaze.

12. Spread half of the glaze over completely cooled brownies, allow it to harden, then spread the remaining glaze on top and let set.

13. Cut into 16 squares and store leftovers in an airtight container.