Step 1: Preheat your oven to 375°F (190°C). Lightly butter a 9x13 inch baking dish or a 2.5-3 quart oven-safe dish.
Step 2: Prepare the blueberry filling. In a large bowl, gently combine the blueberries, 1/2 cup granulated sugar, 2 tablespoons flour, lemon juice, cinnamon, and nutmeg (if using). Pour the mixture evenly into your prepared baking dish.
Step 3: Make the cobbler topping. In a separate large bowl, whisk together the 1 1/2 cups flour, 1/2 cup granulated sugar, baking powder, baking soda, and salt.
Step 4: Cut in the cold butter. Add the cold butter pieces to the dry ingredients. Use a pastry blender, two knives, or your fingertips to cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter remaining.
Step 5: Add wet ingredients to topping. In a small bowl, whisk together the buttermilk and vanilla extract. Pour the wet ingredients into the flour-butter mixture and stir with a fork just until combined. Be careful not to overmix; a few lumps are fine.
Step 6: Assemble the cobbler. Drop spoonfuls of the cobbler topping over the blueberry filling, leaving some gaps for the berries to bubble through. Sprinkle the top evenly with turbinado sugar, if desired, for a sparkling, crunchy crust.
Step 7: Bake the cobbler. Place the baking dish on a baking sheet (to catch any potential overflow). Bake for 35-45 minutes, or until the topping is golden brown and the blueberry filling is bubbly and thick. If the topping starts to brown too quickly, you can loosely tent it with foil.
Step 8: Cool and serve. Remove the cobbler from the oven and let it cool for at least 15-20 minutes before serving. This allows the filling to set up properly. Serve warm with a scoop of vanilla ice cream or a dollop of whipped cream.