I made chili oil with bay leaf, sesame seeds and a bunch of spices/aromatics and have to admit - I don’t really love using it, although I feel it’s legit: https://thewoksoflife.com/how-to-make-chili-oil/
It tastes really strongly of bay leaf and doesn’t have that nice umami flavor that you get from most chili oils. I was pretty careful with the oil temperature, so I’m not sure what factors play role.
The best chili oil sauce I’ve ever had was made by friends of mine; the wife in the couple hails from Sichuan province (I want to say Chengdu), and he’s Taiwanese American. Their recipe is quite simple:
She stressed that the choice of chili flake and the control of the oil temperature are key. I was surprised that she actually uses Kirkland chili flakes and heats the oil to about 355F, then pours it over the peppers (and sometimes Sichuan peppercorn).
Cool to room temperature, mix in soy sauce, sugar and raw minced garlic. Be careful with the sugar as it will become stronger as it dissolves. The ratio of soy sauce, sugar, and garlic is to taste.
I was gifted a jar of this sauce and it is pretty darn amazing. Makes everything taste better. Much better than my own attempt at chili oil, and less complicated. I’m going to try this with some facing heaven chilis I have.