Preheat oven to 250°F. Set racks in upper and lower thirds of oven. Place wire cooling racks in the rimmed baking sheets and place in the oven.

Using a food processor with a grating insert, grate the potatoes and then the onions, transferring grated vegetables to a large bowl when the bowl of the food processor is filled. Alternately, use a box grater. Working in batches, place the potatoes and onions in a clean dishtowel and thoroughly wring out the excess liquid over the sink, then transfer the potato-onion mixture to a large bowl. The more liquid you remove, the crispier your latkes will be, so take your time and use several dish towels if necessary. Reserve the potato-onion mixture.

In another large bowl, whisk together the matzo meal, salt, and pepper. Add the eggs and whisk to combine. Add the potato-onion mixture and mix well.

In a large skillet over medium heat, melt equal parts schmaltz and oil (or oil only if omitting the schmaltz) until a scant ¼-inch depth of fat is reached. Drop 2 tablespoons of latke mixture into the hot fat, spacing them 2 inches apart. Flatten latkes slightly using a spatula and cook, turning once, until crisp, golden brown, and cooked through, 3 to 4 minutes per side.

Transfer latkes to wire racks and season with salt; return to the oven to keep warm; season with salt. As you remove latkes from the pan, replace them with fresh spoonfuls of potato mixture to maintain oil temperature. Add additional schmaltz and/or oil around the edge of the pan as needed to maintain a scant ¼-inch depth of fat.

Keep latkes warm in oven