Preheat your oven to 450F. Heat the cast iron pan for 10 minutes.
In the meantime, peel and shred the potatoes and onion. I use a food processor, but you can do this with a coarse grater.
Squeeze as much of the liquid out of the potatoes as you can and discard the liquid.
Add the rest of the ingredients (except the water) to the potatoes and onion in a bowl. Transfer to the heated cast iron pan. Press the mixture down to compact it. Pour over the boiling water just as you place it in the oven.
Bake for 20 minutes.
Reduce the temperature to 425F and bake for another 35 minutes.
Then turn the broiler on high and broil until browned on top. This should take about 3 minutes.
Rest the kugel for 20 minutes before cutting into it and serving.
Video
Notes
Baking kugel in a cast iron pan isn't traditional, but it is the best way to get a crispy outside. This recipe uses a 10-inch cast-iron skillet.Squeezing the liquid out of the potatoes and then adding boiling water helps make sure the correct amount of liquid is added to the recipe. It also replaces starchy water.Be sure to watch the kugel when broiling. It can burn quickly.