Preheat oven to 425 degrees F (220 degrees C). Grease an 8-inch square baking dish.
Stir cranberries with 1 tablespoon of sugar in a bowl. Whisk flour, cornmeal, 1/2 cup sugar, baking powder, baking soda, and salt in a separate bowl. Whisk milk, eggs, and melted butter together in a third bowl. Pour milk mixture into dry ingredients and stir just until moistened. Stir cranberries into batter; pour into prepared baking dish.
Bake in the preheated oven until corn bread is golden brown, 18 to 20 minutes. Let cool completely in pan before cutting into squares for serving.
