In a medium pot, add the chicken stock, chicken thighs, and salt; simmer gently for 15 minutes, loosely covered, until the chicken is fork tender.
Add the coconut milk, lemongrass, galangal, kaffir lime leaves, Thai chilies, 1 ½ tbsp. of the fish sauce, and palm sugar. Simmer for three to five minutes to infuse. Note: The lemongrass, galangal, and kaffir lime leaves are traditionally left in the soup, but are not meant to be eaten. You can remove them after this step or inform your guests not to eat them.
Add the mushrooms and cook for another one to two minutes to soften. Remove from the heat and stir in 2 tablespoons of the lime juice. Taste and adjust the seasoning with more fish sauce and/or lime juice if needed.
Garnish the soup with chopped cilantro and/or green onions. You can pour the soup over rice, add rice to the soup bowl, or enjoy the soup on its own. This soup is usually mildly spiced, but you can break up the chilies to release more heat.
For the spring rolls
Soak the glass noodles in room-temperature water for ten minutes. Drain, then cut them into short pieces, about five to seven centimeters long, with scissors.
Remove the shiitake mushrooms from the soaking water and squeeze the mushrooms firmly to remove as much water as possible. Finely chop the mushrooms and set aside.
Mix the ground pork with 1 teaspoon of the soy sauce and set aside.
In a wok or large sauté pan, add a little vegetable oil, the garlic, black pepper, and white pepper; stir until the garlic turns slightly golden. Add the pork and cook until no longer clumpy and almost done. Add the shiitake mushrooms, noodles, cabbage, carrots, cilantro stems, sugar, salt, and the remaining 2 teaspoons of soy sauce. Toss until the noodles are fully cooked and the cabbage is wilted, adding a splash of water if the noodles start sticking.
Remove from the heat, taste, and add more salt as needed. Put the filling into a bowl and let cool before wrapping.
To wrap: Place one spring roll wrapper on a clean surface with a corner pointing towards you. Place a heaping 1/4 cup of filling on the wrapper slightly off centre and towards you, and spread the filling out into a log shape, about 12 centimeters long. Pull the corner closest to you over the filling and roll once, making the roll as tight as you can. Keeping the roll in place with one hand, fold the left and right corners inward with the other hand and keep rolling until the side corners are tucked under. Use your finger or a brush to brush the beaten egg along the edges of the remaining wrapper; continue rolling until the end.
To fry: Heat five to seven centimeters of oil in a pot to 350°F. Add the spring rolls and fry until golden brown, about five minutes.
Let cool slightly before serving. You can cut the spring rolls in half on a sharp bias for a nicer presentation. Serve with sweet chili dipping sauce.