Using the coarse side of a box grater or a food processor fitted with a medium-coarse grating disk, grate potatoes, parsnips, and shallots. Toss together in a large bowl.
Add eggs, matzo meal, salt, and pepper to potato mixture and toss to mix well.
Pour 3/4 in. oil into a 10- to 12-in. frying pan (with sides at least 2 in. high) over medium-high heat. When oil reaches 350°, scoop 1/3 cup of potato mixture from bowl, then gently turn onto a wide spatula. Press into a patty about 1/3 in. thick, then gently slide pancake into hot oil. Cook 3 or 4 pancakes at a time (do not crowd pan) until edges are crispy and well browned and undersides are golden brown, 2 to 3 minutes. Gently turn and cook until other sides are golden brown, 2 to 3 minutes longer.
Transfer pancakes to paper towels to drain briefly, then keep warm in a 200° oven while you cook remaining pancakes. Serve hot, with Gingered Sour Cream.
Note: Nutritional analysis is per latke.
Tips for Terrific Latkes:
Soaking, rinsing, and drying the grated potatoes removes excess starch and makes the latkes crispy (not necessary for sweet potatoes). Sweet potatoes are less starchy than russets or Yukon Golds, so there's no need to rinse or squeeze the grated potatoes.
Use restraint when adding eggs and matzo meal. Too much will make the latkes heavy.
Keep oil between 300° and 350° while frying to prevent latkes from turning greasy. Check heat with a candy thermometer and adjust heat accordingly.
If making latkes ahead, let cool on paper towels, then arrange in a single layer in a zip-lock plastic bag and refrigerate up to 3 days. Reheat in a 300° oven until crispy and hot, about 15 minutes.