Cut the top off the garlic bulb roughly 2cm down from the top so the cloves are exposed.
In a small pot, combine the olive oil, garlic and rosemary. Cook on a low heat for 30 minutes or until the olive oil flavour is infused with garlic and rosemary. Carefully strain the oil through a fine mesh strainer into a glass jar. We will not need all of the oil for this recipe and the remaining oil can be stored for 1 week in the fridge and be used in any recipe that calls for olive oil. Set the garlic to the side.
While the olive oil cooks, prepare the potatoes. Place the potatoes in a large pot, cover with cold water and swirl the potatoes around with your hands until the water turns cloudy. Drain the potato and rinse under cold water. Return the potatoes to the pot and cover with cold water, along with a generous amount of salt (roughly 2 tablespoons). Bring to the boil over high heat, then cook the potato for 20 - 25 minutes or until very soft – a skewer or knife should be able to go through them with no resistance.
Reserve up to 1 cup of cooking water. Drain the potatoes in a colander and cover with a tea towel. This will allow the potato to steam and remove as much moisture as possible. Leave to sit for 10 minutes.
Place the potatoes back into the pot they were cooked in and mash with a potato masher. Using a potato masher or wooden spoon, slowly incorporate up to 1 cup of cooking water and up to ½ cup olive oil until the potatoes are at your desired consistency.
Season with salt and pepper. Sprinkle over fresh rosemary and squeeze over the cooked garlic cloves if you desire! Serve immediately or store in a tupperware in the fridge for up to 4 days.