½ cup extra-virgin olive oil
8 tablespoons butter
2 large onions, peeled and sliced in 1/4-inch half moons
3 garlic cloves, peeled and chopped
½ teaspoon kosher salt, plus more for the pasta water
2 ounces canned anchovy fillets, drained and finely chopped
1 cup chicken stock, hot
freshly ground black pepper, to taste
2 pounds fresh bigoli, (see recipe for homemade bigoli pasta)
⅓ cup Italian parsley, freshly chopped
Heat the olive oil and butter in the large skillet over medium heat. When the butter is melted, stir in the onions and garlic, season with 1/2 teaspoon salt, and cover the pan. Let the onions cook slowly, stirring now and then, to release their liquid, soften and shrink. After 15 to 20 minutes, when the onions are concentrated, golden, and edged with brown, add the chopped anchovies, raise the heat, and cook, stirring, for a couple of minutes, as the anchovies melt in the hot oil.
Pour in the stock, bring to a bubbling boil, and cook, stirring, to amalgamate the sauce and thicken it slightly. Season generously with freshly ground black pepper, and adjust salt to taste. Remove from the heat; return to the simmer before you add the bigoli.
Cook the bigoli until nearly al dente in 8 quarts of boiling salted water. Drop the pasta into the simmering onion-anchovie sauce, and toss together for a minute to finish cooking and coat the bigoli. Turn off the heat, toss in the parsley, and serve immediately.