In a large bowl, combine flour, yeast, sugar, baking powder, and salt. Gradually add warm water, vegetable oil, and rice vinegar, stirring until a dough forms.

Transfer the dough to a lightly floured surface and knead for 5–7 minutes until smooth and elastic. Place in a greased bowl, cover with a damp cloth, and let rise for about 45 minutes or until doubled in size.

Heat vegetable oil in a large skillet over medium-high heat. Add cubed beef, season with salt and pepper, and brown on all sides. Remove and set aside.

In the same pan, sauté chopped onion for 3–4 minutes until softened. Add garlic and ginger and cook for another 1–2 minutes until fragrant.

Return the beef to the pan. Stir in soy sauce, hoisin sauce, oyster sauce, brown sugar, rice vinegar, and beef broth. Reduce heat and simmer for 20–25 minutes until the beef is tender and the sauce has thickened. Adjust seasoning as needed.

Punch down the risen dough and divide into 10–12 portions. Roll each into a ball and flatten into a round disc using a rolling pin.

Place a small square of parchment under each disc, fold in half to create the bao shape, and arrange in a steamer with space between each bun.

Steam over boiling water for 10–12 minutes until puffed and cooked through.

Carefully open each bun and fill with the warm beef mixture. Garnish as desired and serve immediately.