1. Peel and grate potatoes and onion. "Don't use a food processor for either one," says Jasinski. "Too much water will come out and it'll be a mess." Mix grated potato with onion, then drain well in a colander about 5 minutes, pressing occasionally to remove liquid.
2. Meanwhile, mix sour cream with zest, juice, and a pinch of salt and pepper. Chill.
3. Whisk together 2 eggs, breadcrumbs, 1 1/2 tsp. salt, the baking powder, and a pinch of pepper in a large bowl. Add the drained potato mixture and stir to combine.
4. Preheat oven to 220°. Heat 2 tbsp. fat in a large frying pan over medium-high heat. Form mixture into patties, using about 1/4 cup of the mixture for each, squeezing gently to expel excess liquid. "You don't want to squeeze all the flavor out of it." Fry patties as you shape them, working in batches of 3. Add 2 tbsp. fat per additional batch and cook patties until deep golden brown, turning once, 5 to 7 minutes per batch. "You can press them gently with a spatula to make them even thinner, so they get crispy all the way through." Transfer latkes to a baking sheet lined with paper towels and keep warm in oven until all are fried.
5. Meanwhile, cook 8 eggs the way you like--fried, scrambled, even poached. Warm chicken confit in the microwave (or in pan with eggs). Put 2 eggs on each of four plates and set 3 latkes alongside. Top each latke with sour cream mixture, 1/4 cup warmed confit, a small spoonful of pear preserves, and a sprinkle of parsley.
Make ahead: Sour cream mixture, 1 day, chilled; latkes, several hours (recrisp in 220° oven before serving).