Char the onions and ginger*. Turn the oven broiler to high, and place the baking rack about 8 inches away from the heating elements. Place the onion and ginger cut-side-up on a baking sheet, and brush with a bit of oil. Broil for about 7-10 minutes, until the tops of the onion and ginger are slightly charred. Remove and set aside. Make the broth. Meanwhile, heat the anise, cloves, cinnamon, cardamom and coriander to a large stockpot over medium-high heat for about 3 minutes until fragrant. Add in the charred onion, ginger, stock, and stir to combine. Continue cooking until the broth reaches a simmer. Then reduce heat to medium-low, cover with a lid, and continue to simmer for at least 30 minutes. Strain out (and discard) the onions, ginger and spices. Stir in the fish sauce and sweetener into the hot broth. Then finally, taste and season the broth with salt as needed. Prep the noodles. Meanwhile, as your broth is simmering, cook the noodles separately al dente according to the package instructions. Drain in a strainer, then briefly rinse the noodles with cold water to prevent them from continuing to cook. (I also recommend tossing the noodles with a drizzle of oil — such as sesame oil — to prevent them from sticking.) Assemble. Now the fun part! Add a handful of noodles to each individual serving bowl. Portion the steak between each serving bowl. Then ladle the still-simmering hot broth into the serving bowls, being sure to submerge the steak completely so that it gets cooked*. Top each bowl with lots and lots of garnishes, and finish with a squeeze of lime juice. Serve immediately. Encouraging everyone to stir the garnishes into the soup so that they can flavor the broth, also adding in additional extra sauces if desired. Garnishes: fresh herbs (cilantro, mint, and/or Thai basil), bean sprouts, lime wedges, thinly-sliced chiles (Thai bird chiles or jalapeños), thinly-sliced onions (green onions or white onions), sauces (hoisin and/or sriracha)