Part 5/9:
Gluten development is critical for panettone's iconic tall and airy crumb. The recipe emphasizes slow, patient kneading to build a strong gluten network. Once the dough pulls away from the sides of the bowl and passes the "windowpane test"—where a thin, translucent membrane Forms when stretching a small piece—it is ready for the next step.
The butter, softened but not melted, is gradually incorporated over the course of 3 minutes of kneading. Adding it in small amounts allows the dough to absorb the fat evenly, resulting in a tender, moist loaf. The process results in a seemingly strange, sticky dough that ultimately becomes supple and tacky—proof of proper gluten development.