Heat a large skillet over medium-high heat.
Add ground pork to a dry pan. Oil is not needed, but if your pork has low fat content, add a bit of neutral oil to help it crisp.
Spread into an even layer and do not touch for 2–3 minutes until deeply browned and fat renders.
Break pork into chunks, leaving some crispy bits intact.
Push pork toward the edges of the pan.
Optional: Crack an egg into the pan off heat and stir quickly for a touch of scrambled egg.
Add cabbage and scallion whites to the center and let it cook in the rendered pork fat.
Cook until softened with light char, about 1 minute.
Add drained rice noodles and fish sauce to the skillet.
Pour in enough chicken broth to just barely cover the noodles.
Scrape the bottom of the pan to release browned bits.
Bring to a strong boil and toss constantly.
As the liquid reduces, pork fat and noodle starch emulsify into a glossy sauce.
Cook until noodles are tender and sauce clings tightly with a small puddle remaining.
Add soy sauce and chili crisp and toss once more.
Taste and adjust seasoning if needed.
Serve immediately while hot and glossy. Finish with sliced scallions if desired.
