Dough: Dilute 1 teaspoon of sugar into warm milk (about 110°F/43°C). Stir in the yeast and let sit for 5 – 10 minutes until it is foamy. If it is not foamy, the yeast is no longer active and unfortunately cannot be used. Whisk in eggs into the yeast mixture to combine.

In a bowl, combine flour, sugar, and salt. Pour in the yeast mixture and mix until it becomes a dough.

Transfer the dough onto a floured surface and knead for 2 minutes. Wrap and knead the softened butter into the dough until it is fully incorporated. It will be messy at first but as long as we keep kneading, the dough will become less greasy and easier to handle. Knead until it becomes smooth, elastic, and not sticky (10-15 minutes).

Round the dough and grease it with vegetable oil. Place in a large bowl and cover with a damp cloth or plastic wrap. Let it rest in a warm area until doubled in size (about an hour).

Filling: Cut the sweet potato into smaller chunks. Steam for 10 minutes or until soft (a fork can go through easily). Mash them with a fork or potato masher. Then combine thoroughly with the other ingredients.

Spread the sweet potato filling throughout the surface. Cut the dough in half lengthwise to get 2 equal portions of 6x16 inch. Carefully stack one on top of the other.

From the short edge, roll the dough until the end to form a short thick log. Slice it into 4 equal portions. Arrange them, cut-side down, in a 9x6 inch (23x15 cm) loaf pan that has been lined with parchment paper. Cover with a damp cloth or a plastic wrap and proof for 1 hour.

Brush the top of the dough with egg wash (lightly beaten egg). Then bake in a preheated oven at 350°F (180°C) for 40-45 minutes. Let cool on a wire rack for 5 minutes. Then remove the bread from its pan to cool completely.