- Toss shredded potato, shredded onion, minced shallots and salt in a medium bowl.
- Transfer to a sieve set over a large bowl; let drain for about 15 minutes.
- Squeeze the potato mixture, a handful at a time, over the bowl to release excess moisture (don’t over squeeze—some moisture should remain).
- Transfer the squeezed potato mixture to another large bowl.
- Carefully pour off the liquid, leaving a pasty white sediment—potato starch—in the bottom of the bowl.
- Add the starch to the potato mixture. Stir in beaten egg.
- Put matzo pieces in a sealable plastic bag and crush with a rolling pin into coarse crumbs.
- Sprinkle the crumbs and pepper over the potato mixture and toss to combine.
- Cover and refrigerate until the matzo is softened, 20 to 30 minutes.
- Preheat oven to 425°F. Coat a baking sheet with cooking spray.
- Heat 1 tablespoon oil in a large skillet over medium-high heat.Stir the potato mixture.
- Cook 4 latkes per batch: place 1/4 cup potato mixture in a little of the oil and press with the back of a spatula to flatten into a 3 1/2-inch cake.
- Cook until crispy and golden, 1 1/2 to 3 minutes per side.
- Transfer the latkes to the prepared baking sheet.
- Continue with 2 more batches, using 1 tablespoon oil per batch and reducing the heat as needed to prevent scorching.
- Transfer the baking sheet to the oven and bake until heated through, about 10 minutes.
- Serve with cheese sauce or mayonnaise.