Put the potatoes into a large saucepan and cover with water. Place over high heat and bring to a boil. Cook until fork tender, about 25 minutes. Drain the potatoes and return to a low heat for 2 to 3 minutes to dry up any excess water.
Put the cream and butter into a small saucepan and place over medium heat. Warm until the butter has melted into the cream.
Using a masher, mash the potatoes in the saucepan. Add the garlic, cream, butter, salt and pepper and mix well using a large spoon. Stir in the truffle oil and serve.