Soak the guajillo peppers in 1 cup of boiling water for about 30 minutes, until softened. Open and remove most of the seeds.
Combine all the marinade ingredients in a blender and pulse until a paste forms.
Add 1-4 tablespoons of the guajillo pepper soaking liquid until the mixture is pourable.
Pour the marinade over the beef shanks and let it sit in the fridge overnight. (I use a ziplock bag to marinate the shanks as it makes it easier to coat all sides of the beef).
Heat a large pot or Dutch oven over medium high heat.
Add the beef shanks (marinade included) and brown on both sides (about 2-3 minutes per side).
Pour in broth, bring to a simmer, cover and simmer for 4-6 hours, until beef shanks are tender.
Strain the broth through a mesh sieve (you can also serve as is, but it won't be as clear).
Serve with cooked ramen noodles and toppings.
Notes
When marinating the beef, I recommend using a large ziplock bag as it makes it easier to coat all sides of the beef shanks.
Browning the beef shanks adds flavor and seals in the juices so be sure not to skip this step.
You’ll need to use a large pot in order to fit the beef shanks and all of the broth.
To control the saltiness of the ramen broth, I recommend using a homemade or low sodium chicken broth.