Preheat the oven to 350°F. Lightly grease an 8x8-inch baking dish.
In a large mixing bowl, whisk together the flour, cornmeal, baking powder, baking soda, salt, and sugar.
Add the creamed corn, vegan sour cream, 6 tablespoon melted vegan butter, and apple cider vinegar. Stir until just combined.
Fold in the drained whole-kernel corn. Don’t overmix.
Spread the mixture evenly into the prepared baking dish. The batter should be thick but very moist and spoonable, considerably wetter than traditional cornbread batter. If it looks unusually stiff, stir in 2–3 tablespoon unsweetened plant milk.
Bake for 45–50 minutes, until the edges and top are lightly golden and the center is set but still looks moist. Don’t wait for the center to become completely dry.
Immediately brush the top with the remaining 1 tablespoon melted vegan butter.
Let the casserole rest for 10–15 minutes before scooping and serving. This is important—it’ll firm up slightly as it sits while staying creamy inside.