1. Preheat oven to 400º. Grease 2 baking sheets liberally with the oil.
2. Pour the buttermilk in a bowl and set aside. In another bowl, beat the egg, then mix in the Worcestershire sauce and the hot pepper sauce (if desired). On a large plate, place 1 cup of flour and season it liberally with salt and pepper.
3. Peel and cut the onion into thick slices, then separate them into rings. Place the rings in the buttermilk and let sit 5 minutes. Remove, then dip them into the egg mixture, coating both sides.
4. Lightly dredge the egg-coated rings in the seasoned flour; shake to remove excess. Add more flour to the plate as needed. Place rings on greased baking sheets. (Up to this point, the recipe can be made several hours ahead. Cover and refrigerate.)
5. Bake the rings on the middle rack of the oven for 8 minutes. Flip and bake for another 7 to 8 minutes, or until golden brown and tender. Sprinkle lightly with salt.
How kids can help: Pour buttermilk in a bowl; mix egg, Worcestershire sauce, and hot pepper sauce.