Set your oven to preheat to 425°F. Put the entire 1/2 cup of salted butter into a 9×13 inch baking dish and place it in the oven as it heats. Allow approximately 10 minutes for the butter to melt completely while the oven reaches temperature. This timing gives you the opportunity to prepare your dry ingredients.

In a large mixing bowl, combine the flour, granulated sugar, baking powder, lemon zest, salt, baking soda, and ground cardamom. Whisk these dry ingredients together thoroughly to ensure the leavening agents, spices, and zest are evenly dispersed throughout the flour mixture, which promotes uniform rise and balanced flavor.

Add the room temperature buttermilk to the whisked dry ingredients and stir until the mixture just comes together. The dough should appear thick and shaggy in texture—resist the urge to overmix, as this will result in tough biscuits. When the oven has reached 425°F and the butter is fully melted, carefully take the baking dish out of the oven and transfer 4 tablespoons of the melted butter from the dish into the dough, stirring gently to incorporate. Keep the remaining butter in the baking dish.

Add the fresh blueberries to the dough and fold them in carefully, taking care not to crush the berries or work the dough too much. Transfer the dough into the hot baking dish containing the reserved melted butter, spreading it evenly across the bottom so the butter surrounds and coats the base. Scatter the turbinado sugar over the entire top surface—this will create a crunchy, caramelized finish. Use your hands or the back of a spoon rather than a spatula to spread the dough, which helps prevent crushing the blueberries.

Place the baking dish in the 425°F oven and bake for 25 minutes, until the top turns golden brown and a toothpick inserted into the center comes out clean. Take the dish out of the oven and allow it to rest for 5 minutes—this brief resting period lets the crumb structure set properly while keeping the biscuits moist. Slice into 9 equal portions and serve while still warm.