Caramelize the Onions to Perfection
Heat olive oil and unsalted butter in a large pot or Dutch oven over medium-low heat. Add thinly sliced yellow onions, along with the initial pinch of salt and pepper. Cook slowly, stirring occasionally, for 30-40 minutes, until deeply golden-brown and caramelized. This step is crucial for developing the profound, sweet, and savory base of the dish.

Build the Savory Sauce Base
Once the onions are caramelized, stir in minced garlic and red pepper flakes for one minute until fragrant. Add Worcestershire sauce and soy sauce. In a separate bowl, whisk evaporated milk and cornstarch until smooth. Pour in water (or beef broth), beef bouillon, and the milk mixture. Add dried parsley, thyme, oregano, paprika, and pepper. Bring to a gentle simmer, stirring constantly until slightly thickened.

Cook the Pasta in the One Pot Method
With the sauce simmering, add the uncooked short-cut pasta (like orecchiette). Stir to submerge all the pasta. Cover the pot and cook according to the pasta package directions, stirring every few minutes to prevent sticking. Continue cooking until the pasta is al dente and most of the liquid is absorbed, leaving a rich, thick sauce.

Finish with Cheesy Goodness
As soon as the pasta is cooked and the sauce has thickened, remove the pot from the heat immediately. Stir in the freshly shredded Gruyere cheese and Parmesan cheese. Continue stirring gently until both cheeses are completely melted, creating a wonderfully creamy, luscious, and cheesy pasta sauce that clings beautifully to every piece of pasta.

Serve and Garnish
Ladle generous portions of the one-pot French onion pasta into bowls. If desired, garnish each serving with a sprinkle of fresh parsley for a lovely pop of color and a fresh, herbaceous note. Serve warm and enjoy!