How to Make It
In a medium saucepan, cover the Yukon Golds with cold water, season generously with salt and bring to a boil. Cook until tender, about 15 minutes. Drain and pass through a ricer into a large bowl.
Peel the russets. Shred them on the large holes of a box grater into a colander. Rinse under cold water, then pat dry with a clean kitchen towel. Add half to the riced potatoes.
In a food processor, pulse the remaining shredded potatoes with the onion until pasty, about 20 times. Transfer to a sieve and press dry. Add to the riced potatoes. Stir in the eggs, matzo meal, pepper and 2 teaspoons of salt.
Line a baking sheet with paper towels. In a large, heavy skillet, heat 1/4 inch of oil over moderate heat to 350°. Working in batches, spoon 2 tablespoons of the batter into the oil for each pancake and press to flatten. Fry, turning once, until golden and crisp on both sides, about 7 minutes. Transfer to the prepared baking sheet and sprinkle lightly with salt. Serve with applesauce, crème fraîche, smoked fish and dill.