Grate the onion and potatoes, using either the large holes on the side of a box grater or a food processor. Squeeze the liquid out of the shredded potato and onion into a small bowl, and put the potato and onion into another bowl. Let the starch settle to the bottom of the small bowl; pour off the liquid, and sco0p the starch into the potato-onion mix.
Using the box grater or a food processor, grate the celery root and add it to the poatoes. Stir in the eggs, flour and salt to taste - about a teaspoon. If mixture seems too runny, add a little more flour.
Coat the bottom of a large nonstick pan with canola oil and heat. Working in 2 batches, drop big heaping tablespoons of the pancake mix (about 6-8) into the pan, and flatten slightly. Cook about 1-2 minutes over medium high flame until crisp; flip, and repeat. Transfer to paper towels to drain. Add a little more oil, and repeat with the next batch.