Preheat your Oven: Start by preheating your oven to 450°F (230°C). This high temperature will help achieve the perfect golden-brown color on your biscuits. Lightly spray a 9-inch square baking tin with non-stick spray.
Add Butter to the Tin: Pour the melted butter into the prepared baking tin, spreading it evenly across the bottom.
Mix Dry Ingredients: In a mixing bowl, whisk together 2 1/2 cups (350g) all-purpose flour, 1/4 cup (50g) granulated sugar, 1 tablespoon baking powder, and 1/2 teaspoon salt until thoroughly combined.
Add Buttermilk: Pour in 1 3/4 cups (420ml) buttermilk and gently stir with a wooden spoon or spatula until a sticky dough forms. If the mixture is too dry, add more buttermilk a tablespoon at a time until just combined.
Incorporate Blueberries: Gently fold in the 1 1/2 cups (190g) fresh blueberries into the dough, being careful not to overmix or smash the berries.
Spread in the Tin: Pour the batter into the buttered baking tin, spreading it evenly to cover the melted butter.
Cut the Dough: Using a sharp spatula or knife, cut the dough into 9 equal squares. This will help portion the biscuits for easy serving.
Bake the Biscuits: Place the tin in the preheated oven. Bake for 15 minutes, then rotate the tin and continue to bake for another 10-15 minutes or until the biscuits are golden brown on top.
Prepare the Glaze: While the biscuits are baking, mix together 1 cup (130g) sifted icing sugar and milk in a small bowl until you achieve your desired consistency for drizzling.
Serve Warm: Once baked, cut along the previous lines again to create square biscuits, drizzle the glaze over the top, and serve warm. Enjoy!