Boil the potatoes in their skin together with the garlic cloves. Drain the potatoes and peel. Don’t worry if bits of peel stay on the potato, it will add a nice texture and color.
In a small saucepan, heat the olive oil and sauté/cook the leek in olive oil together with salt, freshly ground pepper and rosemary, until softened – around 10 minutes.
When the leeks have cooled, gently warm them and then mash together with the potatoes, garlic cloves and remaining ingredients. Season to taste with salt, pepper and olive oil.