01 -
Melt butter with olive oil in a large Dutch oven over medium heat until the butter stops foaming.
02 -
Add thinly sliced onions with salt and pepper, stirring occasionally until deeply caramelized, about 30-35 minutes.
03 -
Monitor onions carefully, adjusting heat or adding more fat if they begin scorching.
04 -
Add minced garlic, pepper flakes, and sauces to caramelized onions, cooking briefly until fragrant.
05 -
Pour in water and half the evaporated milk while increasing heat to high.
06 -
Whisk cornstarch with the remaining milk until smooth before adding to the pot.
07 -
Add bouillon, herbs, and seasonings while bringing the liquid to a boil.
08 -
Add uncooked pasta, reducing heat to a medium-high simmer for 20-25 minutes.
09 -
Stir frequently while the pasta cooks, ensuring it stays submerged in the liquid.
10 -
Check pasta periodically, adding more water if needed until al dente.
11 -
Remove from heat when the pasta is done but the sauce is still liquid.
12 -
Gradually stir in Gruyere cheese until completely melted.
13 -
Add Parmesan cheese, stirring until the sauce is smooth and creamy.
14 -
Taste and adjust seasonings as needed.
15 -
Add additional liquid if desired for a saucier consistency.