Martha's friend Salli LaGrone thoroughly preheats the shortening-coated loaf pan to ensure a crisp, crunchy crust on this dense Southern bread.
Preheat oven to 350 degrees. Place shortening in an 8 1/2-by-4 1/2-by-2 3/4-inch nonstick loaf pan. Transfer to oven until melted.
Sift together sugar, flour, cornmeal, and salt. Combine buttermilk and baking soda in a glass measuring cup, then stir into dry ingredients until combined. Add melted shortening from the loaf pan; stir to combine. Pour batter into the hot loaf pan, and bake until golden brown, 50 to 60 minutes. Transfer to a rack to cool before slicing.