In a Dutch oven, bring 4 quarts water to a boil. Stir in the pasta and 2 tablespoons salt, then cook, stirring occasionally, until just shy of al dente. Reserve about 2 cups of the cooking water, then drain and set aside.

In the same pot over medium-high, combine the oil, fennel seeds, coriander and pepper flakes. Cook, stirring constantly, until the seeds are sizzling and the mixture is fragrant, 1 to 2 minutes. Add the tomato paste and ½ teaspoon each salt and black pepper, then cook, stirring often, until the paste browns and slightly sticks to the pot, 1 to 3 minutes.

Add the anchovies and cook, breaking the fillets into small bits, until fragrant, about 30 seconds. Add 1 cup of the reserved pasta water and scrape up the browned bits, then add the pasta and cook over medium-low, tossing to coat the noodles, until the pasta is al dente, about another 2 minutes; add more reserved water as needed so the pasta is silky and lightly sauced.

Off heat, toss in the parsley (if using), then taste and season with salt and black pepper. Serve drizzled with additional oil.