Separate the head of garlic and peel the cloves.Place them in a small lidded casserole dish or terrine.
Add the thyme, rosemary, sage, and salt, then cover with olive oil.
Place in the oven and let confit for about 40 minutes.Allow to cool.
Transfer the cloves to a clean (ideally sterilized) jar.Using a small sieve, strain the cooking oil over the garlic cloves into the jar.
Seal the jar and store in a cool place.Remove garlic cloves as needed and reseal the jar tightly.If necessary, take the jar out a little while before use so the oil becomes more fluid.