Preheat the oven to 350 degrees.
In a medium mixing bowl, combine the blueberries, lemon juice (squeezed from the lemons), and ¼ cup of sugar. Toss gently until the blueberries are evenly sugared. Set aside.
In a separate mixing bowl, combine the flour, baking powder, salt, and 1 cup of granulated sugar. Use a fork to stir until the ingredients are evenly combined.
Add the vanilla extract and buttermilk to the flour mixture, use a spatula to stir the mixture until a thin batter forms.
Place the butter in the cast iron pan, bake the butter in the pan at 350 degrees until the butter has melted (about 3-5 minutes).
Once the butter has melted, take the pan out of the oven and pour the batter over the butter, do not stir the butter in.
Pour the blueberries over the batter in the pan, do not stir the blueberries in.
Bake the cobbler at 350 degrees for 35 minutes, or until the top is golden brown and a toothpick comes out clean.
Let the cobbler cool for a few minutes before serving, then top with vanilla ice cream and the blueberry syrup.