Preheat the oven to 375°F (190°C) and lightly grease your baking dish or skillet.
Make the blueberry base: In a large bowl, toss the blueberries with sugar, cornstarch, lemon zest, lemon juice, and cinnamon (if using). Pour the mixture into your baking dish and spread evenly.
Prepare the cobbler topping: In another bowl, whisk together the flour, granulated sugar, brown sugar, baking powder, and salt. Add in the cold butter cubes and use a pastry cutter or your fingers to work it into the dry ingredients until the mixture resembles coarse crumbs.
Add wet ingredients: Stir in the milk and vanilla extract until just combined. Don’t overmix — the dough should be thick and slightly lumpy.
Top the berries: Drop spoonfuls of the dough evenly over the blueberry mixture. It doesn’t need to cover the entire surface — leave some gaps for the berries to bubble through.
Bake the cobbler: Place the dish in the oven and bake for 35–40 minutes, or until the topping is golden brown and the filling is bubbling around the edges.
Cool and serve: Let the cobbler cool for about 10 minutes before serving. Best enjoyed warm with a scoop of vanilla ice cream.