Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper or a silicone baking mat.
In a large bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt until evenly combined.
Add the cold butter chunks to the dry ingredients and use a pastry cutter or fork to cut the butter in until the mixture resembles coarse crumbs with pea-sized bits of butter remaining.
Whisk 1 cup milk with the vanilla, then pour into the flour mixture and gently stir until a very wet dough forms.
Fold in the blueberries and toasted slivered almonds gently to avoid crushing the berries.
Generously flour a clean work surface. Spoon the dough onto the floured surface, sprinkle a little flour over the top, and pat or lightly roll it into a 10-inch (25 cm) flat circle.
Cut the circle into 8 equal wedges and transfer them to the prepared baking sheet, spacing them slightly apart.
Bake for 15–18 minutes, or until the scone tops are golden brown.
While the scones bake, stir together the powdered sugar, 1/4 teaspoon almond extract, and 2 teaspoons milk in a small bowl until smooth to make the glaze.
Remove the scones from the oven and let them cool on the baking sheet for about 5 minutes, then drizzle the glaze over the warm scones.