Preheat oven to 350°F. Place the butter in a 9×13 inch baking dish and set it in the oven to melt while the oven heats, about 5 minutes.
In a bowl, toss blueberries with 0.5 cup sugar, lemon juice, lemon zest, and cornstarch until evenly coated; set aside.
In another bowl, whisk Bisquick, milk, 0.5 cup sugar, vanilla, and cinnamon until just smooth; do not overmix.
Remove the hot baking dish and swirl to coat the bottom with melted butter. Pour the batter evenly over the butter. Do not stir.
Spoon the blueberry mixture evenly over the batter. Do not stir; the batter will rise up around the fruit as it bakes.
Bake 40 to 45 minutes, until the top is golden brown and the center is set. A toothpick in the cobbler portion should come out mostly clean.
Cool 10 minutes before serving. Enjoy warm with vanilla ice cream or whipped cream.
Notes
Frozen blueberries work well—do not thaw to avoid excess liquid. For a less sweet cobbler, reduce the sugar by 0.25 cup. If your berries are very tart, add an extra 1.0 tablespoon sugar to the blueberry mixture.