In a large pot, add butter and olive oil over medium heat. Allow them to melt and blend, creating a rich base for your onions.

Add the sliced yellow onions into the pot, sprinkle with salt and pepper. Stir gently to coat the onions in the fats.

Cook for about 30-35 minutes, stirring occasionally, until the onions turn golden brown and become irresistibly sweet.

Stir in the minced garlic, red pepper flakes, Worcestershire sauce, and soy sauce; sauté for 30 seconds.

Pour in water and half of the evaporated milk. In a separate bowl, whisk the remaining milk with cornstarch, beef bouillon, and herbs before adding it to the pot.

Increase the heat to bring the mixture to a boil, then add your chosen pasta. Lower heat and let simmer for 20-25 minutes.

Remove the pot from heat. Gradually stir in the Gruyere and Parmesan cheese, letting them melt into the sauce.

Adjust seasoning to taste and optionally top with fresh parsley before serving.