I use Korean red pepper flake, the same type I use in my kimchi, and it had provided fabulous results. I generally build on flavours like spring onions and lot

I use Korean red pepper flake, the same type I use in my kimchi, and it had provided fabulous results. I generally build on flavours like spring onions and lots of garlic first, pulling them out before leaving black cardamom Sichuan green chilis (for a more woody note) star anise cinnamon and coriander seed for a brighter aroma. I also mix black vinegar and salt in with the chilis first before decanting the seasoned oil atop them. I make a litre at a time but can't ever keep it in the house. The whole effort is 1-2 hours but its mostly just watching the garlic and onion and making sure to pull it out before it burns. The decanting doesn't generate smoke or anything troublesome but beware, the smell of chili oil will permeate the kitchen for about three days.