Ingredients:

  • 2 lb (900 g) yellow onions (about 4 large), thinly sliced
  • 1 tbsp (14 g) unsalted butter
  • 1 tbsp (15 ml) olive oil
  • 1 tsp (4 g) light brown sugar
  • 1 ½ tsp (8 g) kosher salt, divided
  • 4 garlic cloves (12 g), minced
  • 1 tsp (1 g) dried thyme
  • 1 tsp (5 ml) apple cider vinegar
  • 4 ½ cups (1070 ml) low-sodium vegetable broth, divided
  • 12 oz (340 g) rigatoni or other short pasta
  • ¼ tsp (1 g) freshly ground black pepper
  • 4 oz (115 g) Gruyère cheese, shredded (about 1 cup)
  • ¼ cup (25 g) finely grated Parmesan (optional)
  • 1 tbsp (4 g) chopped fresh parsley (optional)

Instructions:

  1. Halve the onions from top to root, peel them, and slice into thin half-moons about ¼ inch (6 mm) thick. Shred the Gruyère on a box grater and finely grate the Parmesan.
  2. Melt the butter with the olive oil in a 5- to 6-quart Dutch oven over medium-low heat. Add the onions, 1 tsp of the kosher salt, and the brown sugar. The onions should sizzle gently, not spit.
  3. Cook for 25 to 30 minutes, stirring every 3 to 4 minutes and scraping the browned bits from the bottom of the pot, until the onions are deep mahogany and jammy. If the pot looks dry before they are done, add 1 tbsp water. If the kitchen smells sharp or acrid, lower the heat. Black, charred bits mean the onions have burned.
  4. Stir in the garlic and thyme and cook for about 30 seconds, until fragrant.
  5. Pour in the apple cider vinegar and ½ cup (120 ml) of the broth. Scrape the bottom of the pot until the liquid has nearly evaporated, about 1 to 2 minutes.
  6. Add the remaining 4 cups (950 ml) of broth, the remaining ½ tsp of kosher salt, the pepper, and the dry rigatoni. Bring to a boil, then reduce to a steady simmer and cook for 12 to 14 minutes, stirring every 2 minutes so the pasta does not stick. The pasta is ready when it is tender and the sauce coats the back of a spoon.
  7. Remove the pot from the heat. Stir in the Gruyère a handful at a time until fully melted, then stir in the Parmesan if using. Taste and adjust the salt.
  8. Rest the pasta for 2 minutes, then garnish with parsley if using. The sauce should look glossy, and the cheese should stretch when you lift a spoonful.