Place the grated potatoes in a large bowl or other food-safe container, fill it with water, and then strain. Repeat this rinsing process 2 or 3 times until the water runs clear, then drain the potatoes, squeezing out as much water as possible.
Combine the rinsed potatoes and grated onion in a large bowl and mix them together with your hands.
Add the matzo meal and mix together, then add the chives. Finally, add the eggs and massage them into the potato mixture until thoroughly incorporated.
Add the salt and pepper and mix it in with your hands.
Heat 2 to 3 tablespoons of oil in a large skillet over medium heat. Working in batches so that the latkes are not crowded in the skillet, take a golf ball-size portion of the potato mixture, flatten it between the palms of your hands, and add it to the skillet. Repeat.
Cook the latkes until they're crisp and brown around the edges, about 3 minutes; then flip and cook for another 2 to 3 minutes, until crisp and deep golden brown all over and still tender inside.
Transfer to a paper towel-lined plate or baking sheet. Repeat with the remaining potato mixture, adding a tablespoon or so of oil between batches.
For the celery root-parsnip latkes: Follow the instructions for the potato version, substituting the celery root and parsnips for the potatoes (and skipping the rinsing step at the beginning) and substituting the parsley for the chives.
Cut the squash into chunks and pass them through the grating disk of a food processor. Then follow the instructions for the potato version, substituting the squash for the potatoes (and skipping the rinsing step at the beginning) and substituting the sage for the chives, and cooking the latkes slightly longer over slightly lower heat (about 4 minutes on the first side and 3 minutes on the second side over medium-low heat).
You can reheat the latkes in a 450 degree F oven in 3 to 4 minutes.
