If my dish requires garlic and/or chilli, I fry that gently first for two or three minutes before adding the veg. The garlic is always finely sliced, never crushed, and must not go brown. I'm not religious about it, but generally I would use about two parts onions (or banana shallots, which I love) to one part celery and one part carrot. Occasionally my dish requires pancetta. If so, I would dry-fry that at the very start, then add the chilli and garlic, then, with a bit of extra olive oil, throw in the veg. I prefer to keep the veg quite chunky, so my sweat phase might take 20 or 30 minutes. I never use butter for this and I think it's a waste to use extra-virgin olive oil. A basic soffritto might not have garlic at all: much, most, maybe, traditional Italian cooking avoids using onions and garlic in the same dish - just olive oil, onions, celery and carrot. One school of thought advocates seasoning the soffritto as it's sweating. I prefer not to do this as later ingredients in the dish, such as Italian sausages or Parmesan, can add salt, not to speak of the pasta, which should have been boiled in water just as salty as the Mediterranean! I find the Schwartz crushed chilli flakes to be excellent and reliable, and a jar lasts for ages. And they're three for two in Sainsburys right now!

By the way, I do all this in my large Le Creuset sauté pan. If ISIS ever invades Cornwall, I would fight to the death in order to hang on to that pan!