Set a large, 1-gallon stock
pot with a pasta insert 3/4 full with water over high heat and bring to a boil. Add 1/4 cup of the salt to the water as it boils. Place the linguine
in the salted water and return to a boil, stirring occasionally. Cook the pasta until nearly al dente
, 10 to 12 minutes. Drain
and set aside, reserving 1 cup of the pasta cooking water.
While the pasta cooks, set a 14-inch saute pan over medium-high heat and add the olive oil
and butter to the pan and, once the butter melts, add the onions
. Cook, stirring occasionally, until the onions have softened and caramelized, 10 to 12 minutes. Add the garlic
to the pan, stirring until fragrant and the anchovies have melted, 2 to 3 minutes. Add the drained pasta and the reserved pasta
cooking water to the pan and season with the remaining 1 1/2 teaspoons kosher salt, pepper, and parsley. Cook, tossing to combine, until the pasta is heated through and the water is nearly evaporated, 3 to 4 minutes. Remove from the heat, sprinkle with the toasted bread crumbs
and toss to combine. Serve while hot.