How to Make It
In a small bowl, whisk the sour cream with the shallot and season with salt and pepper. Cover and refrigerate the shallot cream until chilled, about 30 minutes.
Preheat the oven to 325º. In a food processor, shred the potatoes and the small onion. Transfer to a strainer set over a bowl and season with 1 tablespoon of salt. Let stand for 5 minutes, then squeeze dry in a kitchen towel. Pour off the liquid in the bowl and add the potatoes and onion. Stir in the egg, egg yolk, butter and cornstarch.
Scoop 1/3-cup mounds of the potatoes onto a parchment paper-lined baking sheet and flatten them to 1/4 inch thick. Bake for about 15 minutes, until just set. Let cool. Reduce the oven temperature to 200º.
In a large saucepan, heat 1 1/2 inches of oil to 350º. Working in batches, fry the sweet onion slices until golden, about 4 minutes. Using a slotted spoon, transfer the onions to a paper towel-lined baking sheet to drain; keep warm in the oven.
Reheat the oil to 350º. Working in batches, fry the latkes, turning occasionally, until browned and crisp, about 4 minutes. Transfer the latkes to a platter and garnish with snipped chives. Serve with the fried onions and shallot cream.