Slice the yellow onions into 1/8-inch rings and preheat your Dutch oven over medium heat.

Add butter and olive oil to the pot, then toss in the onions with salt and pepper. Caramelize for 30-35 minutes.

Stir in minced garlic and red pepper flakes. Add Worcestershire and soy sauce, cooking for an additional 30 seconds.

Pour in water and half the evaporated milk, then whisk together cornstarch and remaining milk and add it to the pot with beef bouillon and herbs.

Bring to a boil, add pasta, reduce heat, and simmer uncovered for 11-14 minutes until al dente.

Remove from heat and stir in Gruyere and Parmesan cheese until melted and creamy.