Preheat oven to 180°C. Cut garlic bulb in half horizontally so you get a cross-section of the garlic. Drizzle each cut face with a little olive oil, season with salt and roast in a small dish (you can do this when you’re roasting the chicken) for 40 minutes or until caramelised and soft.
Meanwhile, place milk and rosemary in a small pot and bring to a gentle simmer (but do not let it boil). Turn off heat and leave rosemary to infuse milk.
Place potatoes and the 1 tsp salt in a pot and cover with cold water. Bring to the boil and simmer for about 15 minutes or until potatoes are soft. Drain well and return to the pot.
Squeeze roasted garlic out of its skin (if it is still hot, hold it in a folded-up paper towel so you don’t burn your fingers) and mash with potato using a potato masher. For an extra silky smooth mash, push mashed potato through a sieve or potato ricer.
Remove rosemary from warm milk and add milk and butter to potato. Continue mashing and stirring until potato is very smooth and creamy. Lastly, fold through the cream and season to taste with salt and pepper. Serve with a drizzle of extra virgin olive oil or melted butter.