Peel and boil the sweet potatoes until tender, then mash and set aside.
In a large bowl, combine bread flour, salt, sugar, and dry active yeast.
Add lukewarm milk, mashed sweet potato, and softened butter to the dry ingredients.
Mix well to form a soft dough, then knead on a floured surface for about 10 minutes until smooth and elastic.
Place the dough in a lightly greased bowl, cover with a damp cloth, and let it rise for 45 minutes or until doubled in size.
Preheat the oven to 180°C (350°F).
Punch down the dough and shape it into a loaf; place it into a greased bread pan.
Cover and let it rise again for 20-25 minutes.
Bake in the preheated oven for 25-30 minutes or until the crust is golden and the bread sounds hollow when tapped.
Remove from the oven and cool on a wire rack before slicing.