Combine scallion whites and light greens, celery root and water in a medium saucepan. Cover and bring to a boil; reduce soup to a simmer and cook 15 minutes or until celery root is tender. In batches, blend vegetables with scallion greens; season soup with salt, pepper and lemon juice.
While soup simmers, heat oil over medium-high. Add parsley leaves to hot oil and cook until crispy and oil turns green, 1 to 2 minutes. Serve soup warm or chilled, garnished with parsley oil and fried parsley leaves.
Before her diagnosis, Caroline wrote a book on cakes called Cake Magic!. She started developing a birthday cake using her gluten-free mix found in that book. Check out other recipes she’s developing for her new life—and the stories behind them—on her blog, The Wright Recipes. Her next book, Catalan Food, written with chef Daniel Olivella, comes out in early September from Clarkson Potter.