Special equipment: a fine-mesh sieve
Position an oven rack on the highest setting and preheat the broiler. Bring a large pot of salted water to a boil.
On a baking sheet, toss the onion and ginger with the canola oil. Broil on high until the onion starts to char and blacken around the edges, rotating the pan and tossing the aromatics halfway through cooking, about 8 minutes.
Heat a large pot over medium-high heat. Working quickly to prevent burning, add the five-spice powder and toast until fragrant, about 10 seconds. Immediately add the broth and 2 cups water, then stir in the charred ginger and onion. Bring the mixture to a boil, then reduce the heat to maintain a simmer and cook until the broth is fragrant and the flavors are concentrated, about 25 minutes.
Meanwhile, cook the rice noodles in boiling water until soft, about 5 minutes. Drain well and reserve in a bowl.
Strain the broth through a fine-mesh sieve, then return the soup to the large pot, stir in the fish sauce and bring to a simmer.
Divide the rice noodles between four large serving bowls. Fan about 4 of the beef slices over the noodles, overlapping slightly. Ladle 2 1/2 cups broth over the meat and serve immediately with the bean sprouts, basil, cilantro, hoisin, scallions, jalapeno and lime at the table.
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