Preheat your oven to 350°F (175°C). Generously grease a cast iron skillet with bacon grease, spreading it around the bottom and sides. Place the skillet in the oven for 7–8 minutes to melt the grease and get the pan hot.
While the skillet heats, mix the cornmeal mix, salt, buttermilk, vegetable oil, and egg in a large bowl. Stir with a spatula until just combined—the batter will come together quickly.
When your skillet is hot, remove it carefully from the oven. Pour in the cornbread batter; you should hear a little sizzle—this gives the cornbread a crisp, golden crust.
Return the skillet to the oven and bake for 20–25 minutes, until the top is golden brown and the edges are crisp (the bottom crust will be even darker and crunchier).
Let the cornbread cool slightly, then flip it out onto a plate so the beautiful brown crust is on top. Slice and serve; it holds together well and is perfect for floating in a bowl of beans or soup.
To clean your skillet, just wipe it out with a paper towel—no need for deep washing if you keep it well-seasoned.