Preheat oven to 350 degrees F. In a bowl, whisk together cornmeal, onion powder, and salt. Add water and whisk well to combine until there are no lumps; batter will be thin and runny.
Pour bacon fat into the pan, coating the bottom in an even layer. Pour the cornbread batter into the center of the pan, allowing it to spread out untouched. (There will be a layer of bacon fat on top of the batter; this is normal.) Bake for 30 minutes.
Cornbread is done when the edges are deep brown and gently curling inwards. Remove from oven and pour off remaining fat (which can be discarded or reserved for another use); let rest, 10 minutes. Flip the cornbread onto a flat work surface. Pat with paper towels to absorb extra grease. Cornbread will be dense, rich, and crisp on the edges. Slice into 8 squares and serve with butter (optional, but indulgent!).