Put the potatoes in a large pot and cover by 1-inch with cold water. Bring the water to a boil over high heat, add salt, to taste, and cook until the potatoes are tender, about 20 minutes.
Meanwhile, create a boat shape out of aluminum foil and add the garlic cloves. Season with salt and pepper, to taste, and drizzle with oil. Seal the foil and roast until the garlic is nicely caramelized, about 30 minutes. Heat the half-and-half in a small saucepan over low heat until hot.
Drain the potatoes and put them back into the pot. The heat from the pot will continue to dry out the potatoes. Add the half-and-half, butter and roasted garlic and mash. Fold in the apples and season, to taste, with salt and pepper. Transfer to a serving bowl and serve.