Place your cast-iron skillet in the middle rack in your oven and preheat to 400 degrees.
In a large bowl, thoroughly whisk all of your dry ingredients together. In a separate bowl, gently whisk the eggs, then add the remainder of your wet ingredients (including the stick of butter) and whisk together.
Add the wet ingredients to the dry and stir with a wooden spoon until all ingredients are wet. Do not overwork. That'll make your cornbread dense. A few clumps are okay.
Carefully remove your skillet from the oven and add the shortening. Swirl until melted.
Pour in the batter. It'll make a sizzling sound as it makes contact with the pan. Gently level the top, then place back in the oven. Bake for 25-35 minutes, until a toothpick poked into the center comes out clean.