Preheat oven to 425 degrees.
Place an 8-inch cast-iron skillet in a 425-degree oven to heat up for at least 10 minutes.
Cut the kernels off the corn cobs and place them in a large bowl. Use the blunt edge of your knife to scrape the milky liquid from the cobs into the same bowl. Add the cornmeal and salt to the bowl and stir well to combine.
Place the bacon fat (or olive oil) in the scorching-hot skillet and tilt the skillet so that the fat coats the bottom and sides. Add the corn mixture and pat down in an even layer. Roast (middle rack) in the oven for about 30 minutes.
Use a round-edged knife to loosen the edges of the corn, and a flexible spatula, as needed, and carefully invert the corn onto a serving platter. Serve right away.