Preheat oven to 400°F. Heat butter in a medium saucepan over high heat; add onion and cook until soft, about 3 minutes. Stir in pasta to coat with oil, then wine; cook until wine has evaporated, about 1 minute. Stir in 2 cups stock and season with salt and pepper; cover saucepan and transfer to the oven to bake 15 minutes.
As risotto bakes, heat oil in a medium skillet over medium heat. Add spinach and peas and cook, tossing occasionally, until spinach wilts and peas are warmed through, about 2 minutes. Season with salt and pepper.
Stir mascarpone into risotto. Serve risotto topped with spinach and peas.
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.