Preheat oven to 450°F.
In a small bowl, combine ¾ cup of raspberries with 2 tablespoons of granulated sugar. Gently toss and set aside.
In a medium bowl, whisk together flour, baking powder, and the remaining 1 tablespoon of granulated sugar.
Pour the buttermilk into the dry ingredients and stir gently until just combined—do not overmix. Fold in the sugared raspberries and their juices.
Pour the melted butter into an 8×8-inch baking dish. Transfer the dough into the dish and gently spread to the edges. Use a knife to lightly score the dough into 9 squares (3×3).
Top with the remaining ¼ cup of raspberries. Bake for 30–32 minutes, or until the tops are golden brown and the edges crisp.
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.