Preheat oven to 350°F (175°C).
Place sliced butter in a 9x13-inch baking dish and let it melt in the oven.
Combine blueberries, sugar, and lemon zest in a small bowl.
In another bowl, mix flour, sugar, baking powder, and salt. Stir in milk until just combined.
Pour the batter over the melted butter in the baking dish.
Spoon the blueberry mixture evenly over the batter and sprinkle lightly with cinnamon.
Bake for 35–40 minutes, until the top is golden and the edges are bubbling.
Let the cobbler rest for 10 minutes before serving warm with ice cream or whipped cream.