Activate yeast in warm water with sugar. Let stand 5 minutes.

In a large bowl, combine flour. Add yeast mixture and oil. Mix and knead until a smooth, elastic dough forms, about 8-10 minutes.

Place dough in a lightly oiled bowl, cover, and let rise in a warm place for 1 hour, or until doubled in size.

While dough rises, prepare the filling. Cook pork belly slices in a pan until crispy. Drain excess fat and set pork aside.

In the same pan or a separate one, combine soy sauce, rice vinegar, grated ginger, minced garlic, sesame oil, and brown sugar. Bring to a gentle simmer.

Return the cooked pork belly to the sauce, stirring to coat thoroughly. In a small bowl, mix cornstarch with a tablespoon of water to create a slurry. Add slurry to the pork mixture and cook until the sauce thickens.

Once dough has risen, gently punch down to release air. Divide the dough into 8-10 equal portions. Roll each portion into an oval shape, about 4-5 inches long.

Place a spoonful of the prepared pork filling in the center of each oval. Fold the dough over the filling and carefully pinch the edges together to seal, forming a bun.

Line a steamer basket with parchment paper or cabbage leaves. Arrange the buns in the steamer, ensuring there is enough space between them for expansion.

Bring water to a boil in the bottom of the steamer. Once boiling, place the steamer basket with buns over the boiling water. Steam for 15-20 minutes, or until the buns are puffed and cooked through.

Serve the homemade steamed bao buns hot and enjoy!