Heat oven to 170ºC.
Cut the top off the garlic bulbs and place in baking foil. Brush with olive oil and close the foil over to form a small tent. Roast 45 to 60 minutes and remove from oven to cool
Once cool, squeeze out the roasted garlic from the bulbs. The garlic does slip out quite easily.
Put butter, roast garlic and salt in a bowl and beat together with a wooden spoon until fully mixed into a smooth consistency.