Preheat the oven to 450°F.
In a small bowl, combine ¾ cup of blueberries with 2 tablespoons of granulated sugar. Set aside.
In a medium bowl, whisk together flour, baking powder, and the remaining tablespoon of granulated sugar.
Pour the buttermilk into the dry ingredients and stir until mostly combined, being careful not to overwork the dough.
Fold in the sugar-coated blueberries, including any liquid from the berries.
Pour the melted butter into an 8×8-inch baking dish. Transfer the dough into the dish and evenly spread it to the edges.
Score the unbaked dough into 9 squares (3×3 pattern). Top with the remaining ¼ cup of blueberries. Bake for 30-32 minutes, or until the tops are golden brown.
While the biscuits bake, make the glaze. In a medium bowl, combine the confectioners’ sugar and milk. Add more milk as needed to reach your desired consistency.
Once the biscuits are done, remove them from the oven. Let the biscuits cool completely before adding the glaze.
Once the glaze is added, cut into squares along the scored lines and serve.