Heat oven to 400º F. Line a large rimmed baking sheet with parchment and place prosciutto on sheet in a single layer. Bake prosciutto until crispy and beginning to brown, 12 minutes. Let prosciutto cool on baking sheet until cool enough to handle, about 5 minutes.
Meanwhile, slice Brussels sprouts and apples. Combine vegetables and mustard seeds in a large bowl. Crumble in prosciutto. Drizzle vinegar and oil over salad and toss to combine. Season with salt and pepper.
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.