1. Bring a large pot of salted water to a boil and cook pasta according to the package for al dente. Drain, rinse under cold water and refrigerate until ready to use.
2. In a large pot, place eggs in a single layer and cover with cold water. Bring to a rolling boil over medium-high heat, turn off heat, cover and allow to sit for 10 minutes. Drain eggs and transfer to a bowl of ice water to stop eggs from cooking further. Peel eggs and slice each in half lengthwise. Separate yolks and whites from 8 egg halves and place in a large bowl. Roughly chop reserved egg whites and remaining egg halves into about ½” pieces, set aside.
3. In the bowl with the egg yolks, add mayo, mustard, vinegar, and sugar. Mash and mix with a fork until smooth, breaking up any lumps. Fold in chilled pasta, celery, celery leaves, fennel, fennel fronds, onions, chopped eggs and season with salt and pepper to taste. Transfer to a serving bowl and garnish with sliced scallions and sprinkle with paprika.

Tip: for an extra cold and crisp snap, keep the sliced celery, fennel leaves and fronds in an ice bath until you’re ready to use.