Silver Dollar Latkes

Place a wire rack in a rimmed baking sheet; line with 2 layers of paper towels. Combine breadcrumbs, salt, baking powder, and pepper in a small bowl.
Using the large holes of a box grater or a food processor, grate potatoes and onions. Transfer to a large kitchen towel. Gather ends of towel in each hand and twist over sink, wringing out as much liquid as possible. Open towel; toss mixture to loosen. Wring out again (excess moisture will lead to soggy latkes).
Transfer potato mixture to a large bowl; add breadcrumb mixture and egg. Toss with your hands to thoroughly combine.
Preheat oven to 425°F. Heat 2 Tbsp. schmaltz and 2 Tbsp. oil in a large skillet over medium-high. Drop a small amount of latke mixture into skillet. If the fat sizzles around the edges, it's ready (do not let it smoke). Working in 5 batches and adding more schmaltz and oil to skillet as needed to maintain about 1/8" fat, drop small spoonfuls of mixture into pan, pressing gently with the back of the spoon or a spatula to flatten slightly. Cook latkes, occasionally rotating pan, until golden brown and cooked through, about 2 minutes per side. (You may occasionally need to pick out stray potato bits from oil if they start to burn.)
Transfer latkes to prepared rack and let drain. Remove paper towels and bake latkes in oven until all are warmed through and recrisped, about 5 minutes.