Place the potatoes in a large saucepan with cold, salted water to cover and bring to a boil over high heat. Reduce the heat to medium and simmer until the potatoes are tender, 30 to 35 minutes; drain.

Meanwhile, in a small saucepan over medium heat, heat the cream, butter, and oil together until just simmering and remove from the heat.

In the bowl of an electric mixer with a whisk attachment (or with a hand-held electric mixer), beat the potatoes and garlic on low to medium speed. Slowly add the cream mixture and mix on medium speed, scraping the bowl occasionally, until smooth. Season with salt and pepper.

Variation:

Lighten the heavy cream with half-and-half or milk, depending on the richness desired.