How to Make It
In a large pot of boiling salted water, blanch the celery for 1 minute. Using a slotted spoon, transfer to a colander and refresh under cold water. Bring the water back to a boil. Add the pasta and cook until just al dente.
Meanwhile, melt the butter in a large skillet. Add the shallot and cook over moderate heat until softened, about 2 minutes. Add the chicken stock, crushed red pepper and celery and cook until reduced by one-third, about 5 minutes.
Drain the pasta, reserving 1/4 cup of the cooking water. Add the cooking water and Parmesan to the skillet and simmer for 2 minutes. Add the pasta, simmer for 1 minute and remove from the heat. Add the chives and lemon zest, season with salt and pepper and toss. Transfer the pasta to a large warmed bowl, sprinkle with the celery leaves and serve.