Shred potato, then the onion, using the shredder attachment on a food processor. Alternatively, use a box grater (and actually earn your latkes!).
Drain any apparent liquid from the food processor bowl, then empty shredded mixture into the center of a dish towel. Fold opposite ends over to enclose the bundle and tie one end to a wooden spoon to give better leverage in wringing every last drop out the mixture. Squeeze over a large bowl, twisting opposite ends and periodically tightening your grip to express all liquid from the bundle. When you've squeezed as much as you can, pour off all liquid from the bowl and unwrap the mixture.
At the bottom of the bowl remains the potato starch - keep that, as it's useful in binding ingredients together. Add to it the eggs, breadcrumbs, salt, pepper, and baking powder, and whisk to incorporate. Add in the shredded potato-onion mixture and stir to coat all until uniform.
Preheat oven to 250 degrees and place a wire rack lined with absorbent paper onto a baking sheet. In a shallow pan, heat sunflower oil and schmaltz over medium heat. Test temperature by dropping a single wisp of potato - it should sizzle upon contact.
Using 1/2 cup scoopfuls shallow fry latkes in batches, turning after 5 minutes or when the outer edge is golden and crispy. Brown on second side - lowering heat as needed - then transfer to oven to keep latkes warm as subsequent batches cook. Serve latkes immediately with traditional garnishes such as applesauce and sour cream. For an extra flourish, add trout caviar or lox and a sprinkle of fresh chives.