Preheat the oven to 170°C (150°C fan) | 325°F | gas 3.
Place two 1 lb jam jars in the oven with their lids to sterilise for 10 minutes. Remove after 10 minutes and place on a heatproof surface or mat.
Use the heel of your palm to crush the garlic bulbs so that the cloves start to separate. Fill each jar with a bulb of garlic cloves and fill with the chillies.
Place the rosemary in one jar and the thyme in the other. Fill with the olive oil before sealing well.
Let the garlic marinate for 2-3 weeks before using.