Gently mash the blueberries with a fork or pulse a few times in a food processor until mostly smooth but still flecked with little bits.

If your berries are very watery after thawing, drain a touch so the puree isn’t too runny.

Place the blueberry puree in a small saucepan over medium-low heat. Stir and let it simmer until it thickens slightly, about 6–8 minutes.

Taste and add a pinch of sugar if your berries are especially tart. Remove from heat and cool a little while you prep the rest.

Preheat the oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy lifting, and lightly butter or spray the paper.

In a mixing bowl, whisk together the melted butter and granulated sugar until glossy. Add eggs one at a time, whisking until smooth.

Stir in ½ teaspoon vanilla and the cooled blueberry puree until the batter is even and rosy.

Whisk the sifted all-purpose flour with the ½ teaspoon sea salt. Fold the dry mix into the wet ingredients gently—don’t overmix.

Spread the batter into the prepared pan and smooth the top. Bake for 25–30 minutes, or until a toothpick inserted near the center comes out with moist crumbs.

Let the brownies cool completely in the pan on a wire rack.

Whisk the sifted powdered sugar with the 2 tablespoons milk, ⅛ teaspoon vanilla, and a pinch of salt until silky.

If it’s too thick, add another teaspoon of milk; if too thin, add more powdered sugar.

Pour the glaze over the cooled brownies and spread evenly. Let the glaze set for 15–20 minutes.