For the garlic confit: In a small saucepan over medium-low heat, simmer the garlic cloves in the oil until tender, 15 to 20 minutes. Let cool. Store in an airtight container in the refrigerator up to 2 weeks.
For the mashed potatoes: Scrub and wash the potatoes, then place in a large stockpot and add cold water to cover. Season the water with 3 tablespoons salt and bring to a boil. Cook until the potatoes are easily pierced with a fork, 25 to 30 minutes. Drain, and let cool for 2 to 4 minutes. Gently peel off the skins and transfer the potatoes back to stockpot.
In a small saucepan over low heat, warm the half-and-half and butter just until the butter is melted, about 2 minutes.
Add the half-and-half mixture and 8 cloves of the garlic confit to the potatoes. Using a potato masher, mash until creamy. Season with the white pepper and 2 teaspoons salt.