Preheat the oven to 325 degrees Fahrenheit.
In a bowl, mix the cornmeal, gf flour, baking soda, baking powder, salt and cornstarch. Set aside.
Mix the nondairy milk and apple cider vinegar and set aside for a couple of minutes.
In a large bowl or the bowl of a stand mixer fitted with the whisk attachment, beat the sugar, butter and applesauce until well mixed. Add the milk and vanilla and mix in.
Add the flour mixture to the wet mixture in two batches, mixing well after each addition. Use a spatula to scrape down the sides and the bottom of the pan to make sure everything is mixed in.
Butter or spray with cooking spray a 10-inch cast iron skillet. Pour the batter into the skillet and smooth down the top with a spatula.
Sprinkle on as many berries as you wish, leaving the rest to serve alongside the cake.
Bake 1 hour or until a toothpick in the center of the cake comes out clean or with a few crumbs adhering to it.
Cool on a rack for 30 minutes to an hour before serving.