Preheat your oven to 375°F (190°C). Lightly grease a 9x9 inch baking dish or a 2-quart casserole dish.

Prepare the filling: In a large bowl, gently toss the sliced nectarines with granulated sugar, cornstarch, vanilla extract, cinnamon, and lemon juice until evenly coated. Pour the mixture into the prepared baking dish and spread into an even layer.

Prepare the topping: In a separate medium bowl, whisk together the flour, brown sugar, baking powder, and salt.

Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. Stir in the milk until just combined; be careful not to overmix the dough.

Drop spoonfuls of the topping evenly over the fruit filling, leaving small gaps for steam to escape. Sprinkle the entire surface generously with coarse turbinado sugar for that golden crunch.

Bake for 35 to 40 minutes, or until the fruit filling is bubbly and thick, and the crust topping is golden brown. If the edges brown too quickly, cover loosely with foil.

Remove from the oven and let the cobbler cool on a wire rack for at least 15 minutes before serving. Best served warm with a scoop of vanilla bean ice cream or fresh whipped cream.