Step 1:
Position a rack in the center of your oven and preheat it to 375°F (190°C). Place the butter in a 10-inch cast iron skillet and transfer the skillet to the oven, allowing the butter to melt completely.
Step 2:
While the butter melts, combine the cornmeal, flour, sugar, baking powder, salt, and baking soda in a large mixing bowl. Add the eggs and buttermilk to the dry ingredients and whisk until the batter is smooth and well-integrated.
Step 3:
Carefully remove the skillet from the oven, ensuring the butter is fully liquefied. Pour about three-quarters of the melted butter into the batter and stir until incorporated. Transfer the prepared batter into the hot skillet, then evenly distribute the cranberries across the surface.
Step 4:
Return the skillet to the oven and bake for 25 to 30 minutes, or until the edges of the cornbread are golden and a toothpick inserted into the center emerges clean. Serve the cornbread warm, accompanied by additional butter if desired.