The CDC note that when chopped garlic in oil is stored improperly, botulism can occur. The same is true for herbs in oil too. Their recommendation is to refrigerate any garlic in oil as soon as possible and discard after four days. Whilst the garlic is whole in this recipe I still approach with caution and make a small batch whenever I'd like it. It takes no effort at all, just a little time in the oven. I've seen some videos of an entire baking dish of confit being made at once... and I have to say that makes me nervous. My recommendation is small batch only.