Slice the flank steak against the grain on a 45-degree angle into ¼-inch thin strips. Transfer the beef strips to a large bowl. (For easier slicing, place the beef in the freezer for 45-60 minutes, uncovered, until the exterior is slightly firm. Then thinly sliced with a sharp knife).
Add the marinade ingredients as listed above to the beef and mix it into the beef. Marinate for 15-20 minutes.
Add the satay sauce ingredients as listed above into a blender or food processor. Blend until you have a very smooth paste. (If you don't own a blender, finely mince the aromatics before mixing with the remaining sauce ingredients).
Heat vegetable oil in a large non-stick pan on medium heat. Fry the beef until it's mostly brown and the center is still pink, about 5 minutes.
Then add in satay sauce and toss everything together. Cook for 1-2 minutes until beef is cooked through and no longer pink. Remove and set aside.
In a large pot filled with enough water, bring to a boil on medium-high heat. Boil rice vermicelli noodles until al dente, about 2-3 minutes. Strain and rinse with cold running water. Then strain again. Divide the noodles into 5 large serving bowls.
Equally divide the cooked satay beef and place on top of cooked noodles and set aside.
In a large pot, combine the broth ingredients as listed above. Bring to a boil on medium-high heat. Once the broth comes to a boil, divide and ladle it over the noodles. Enjoy hot.