After yeast puffs, slowly mix in flours. Then add puréed sweet potatoes, cooled milk, egg, salt and rosemary. Mix to combine ingredients, and then knead dough in mixer or turn out onto a lightly floured surface and knead by hand for 3–5 minutes. Add more flour as needed (up to ¼ cup more) to create a dough that’s soft and pliable and that bounces back slightly when pressed with a finger.