Step 1: Preheat your oven to 400°F (200°C). Pour the melted butter into a 9x9 inch baking dish, tilting to ensure the bottom is evenly coated. Set aside.
Step 2: In a large mixing bowl, whisk together the 2 cups of flour, granulated sugar, baking powder, and salt.
Step 3: In a separate small bowl, gently toss the fresh or frozen blueberries with the 1 tablespoon of flour. This helps prevent them from sinking.
Step 4: Pour the milk into the dry ingredients and stir with a spoon or spatula until just combined. The dough will be very wet and shaggy. Gently fold in the floured blueberries.
Step 5: Carefully pour the wet biscuit dough into the prepared baking dish over the melted butter. Spread it gently and evenly to reach the edges of the pan. Do not press down too firmly.
Step 6: Bake for 25-30 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Step 7: While the biscuits are baking, prepare the lemon glaze. In a medium bowl, whisk together the powdered sugar, 2 tablespoons of lemon juice, and lemon zest. Add more lemon juice a teaspoon at a time until you reach a smooth, pourable consistency.
Step 8: Once the biscuits are done, remove them from the oven and let them cool in the pan for about 10-15 minutes. This allows them to set slightly.
Step 9: Drizzle the lemon glaze generously over the warm (but not hot) biscuits. Slice into 9 squares and serve warm or at room temperature.