Place the potatoes in a large pot of salted, cold water and bring to a boil. Reduce the heat and simmer until the potatoes are fork tender, about 20-25 minutes. Drain the potatoes and return to the hot pot. Place the pot back on the stove and cook over high heat, stirring occasionally until the potatoes are dry and are no longer steaming, about 2 minutes.

While the potatoes are cooking, heat the half-and-half in a small saucepan with the butter and garlic until hot. Remove the garlic and discard.

Mash the potatoes and 2 teaspoons salt with a potato masher or handheld mixer until almost smooth. Add most of the half-and-half and beat until smooth and creamy. Add more half-and-half if needed (save the rest in case you need to reheat the potatoes later). Add the truffle oil and 1 teaspoon pepper. Taste and adjust seasoning with more salt and pepper, if desired. Transfer to a serving bowl and garnish with chopped chives.