French Onion Pasta

Name: French Onion Pasta
Ingredients: 4 tablespoons unsalted butter; 2 tablespoons neutral cooking oil (such as canola oil); 4 large (12 ounces each) red onions , thinly sliced (about 10 cups); 2 teaspoons kosher salt , divided; 1/4 cup dry sherry; 1 tablespoon all-purpose flour; 2 cups unsalted beef or chicken broth; 2 tablespoons Worcestershire sauce; 1 teaspoon fish sauce; 3/4 teaspoon black pepper; 4 (5-inch) thyme sprigs; 1 (2 1/2-inch) fresh or dried bay leaf; 1/2 cup Parmigiano-reggiano cheese , grated (about 1/2 cup packed); 2 ounces Gruyère cheese , shredded (about 1/2 cup); 1 ( 12 - ounce ) package bucatini pasta; 2 tablespoons unsalted butter; 3/4 cup panko (Japanese-style breadcrumbs); 2 teaspoons fresh thyme leaves, plus more for garnish; 1 small garlic clove , grated with a Microplane grater (about 1/2 teaspoon); 1/2 teaspoon kosher salt; 1/2 teaspoon black pepper; 1 ounce Gruyère cheese , finely grated with a Microplane grater (about 2/3 cup), plus more for garnish