Make the Dough:

1. In a large bowl, whisk together flour and salt to combine. Slowly add in boiling water and stir well with a silicone spatula to combine, until there are no dry flour particles visible in the bowl. Make sure to scrape down the sides of the bowl. Cover and let the mixture rest for 10 minutes. (Adding hot boiling water in flour is a technique known as flour scalding, which breaks down starch in the flour and makes the dough softer and more stretchy. It also makes the dough much easier to knead.)

Knead the Dough:

1. Transfer the dough onto a clean and lightly greased surface. The oil will help keep the dough from sticking to your hands initially. You can even lightly oil your hands too.
2. Knead the dough for 5-10 minutes until the dough is smooth and not sticky at all.
   • To knead, push the dough down and outward using the palms of your hands. Fold the dough in half toward you and press down. Repeat this motion by pushing the dough down and outward, and then folding over towards you. This helps build up gluten strength in dough that is responsible for making the bread fluffy.
   • It should take less than 10 minutes of kneading by hand to achieve a non-sticky and smooth dough ball. A well-kneaded dough is smooth and can hold its shape. You can test the dough by giving it a firm poke with your finger. The indentation should bounce right back. If it doesn’t bounce back and stays like a dimple, keep kneading for a few more minutes.
3. Transfer the smooth dough back in the mixing bowl and cover with cling wrap. Let rest for 20 minutes, while you are prepping the filling.

Make the Filling:

1. Soak the vermicelli in hot water for 1 minute, or in colder water for 2-3 minutes, until softened. Drain and finely chop (about 1/4 or 1/2-inch pieces).
2. In a large skillet or wok, heat oil over medium high heat for 1-2 minutes until the oil is hot and starts to sizzle.
3. Add in all the filling ingredients: vermicelli, mushrooms, carrots, green onions, garlic, soy sauce, sesame oil, white pepper, vegetable stock powder (optional), and salt. Stir well with a wooden spatula to mix evenly, about 2 minutes. If you find the vegetable mixture is a bit watery, add a teaspoon of cornstarch to thicken it a bit. Transfer the mixture onto a plate and let it cool down to room temperature, about 15-20 minutes

Assemble the Buns:

1. On a lightly floured surface, roll the dough into a log and divide it into 10 equal pieces using a bench scraper or knife. Take one piece of dough at a time and flatten it with a small dough roller or with your palm.
2. Shape the dough into a 4-inch circle. Note that the centre should be slightly thicker than the edges. This dough should be particularly softer and more pliable because of the hot water scalding flour technique.
3. Place 1 tablespoon of filling into the middle of each rolled out dough. Bring the edges of the dough up, enclosing the filling, and pleat the edges together into a little bag to seal the mixture inside.
4. Add sesame seeds into a shallow dish. Dab the smooth side of the bun with a little bit of water and gently press it into the shallow dish of sesame seeds. The water will help the seeds stick to the bun.
5. Place the bun on a baking tray and cover with a tea towel to prevent it from drying out.
6. Repeat this step with all the buns.

Pan Fry the Buns:

1. In a large non-stick skillet, heat oil over medium high heat for 2 minutes. Place a batch of 5 buns with the sesame seeds side facing up and placed 1/2-inch apart to prevent them from sticking together. Cook for 1 minute until the bottom turns golden brown.
2. Turn the buns over and add 1/2 cup of water into the pan. The water should start sizzling and boiling immediately. Make sure the water is about 1/2-inch deep and covers about one-third of the buns’ height.
3. Cover with a lid and cook covered for 5-6 minutes until almost all the water has evaporated. Because the vegetable fillings are previously cooked, it takes approximately only 5 minutes to fully cook the buns.
4. Take off the lid and lower heat to medium. Cook for another 1 minute until all the water has been absorbed and the sesame seeds side has turned golden brown and crispy as well.
5. Transfer the buns onto a plate and repeat the same method with the second batch.
6. Serve them hot with a side of vinegar dipping sauce.

Make the Vinegar Dipping Sauce:

1. In a small bowl, combine black vinegar, soy sauce, sesame oil, and green onions. Stir with a spoon.
2. Serve alongside the crispy bottom vegetable buns, for dipping.