Peel potatoes and cut into eighths, cover with water, and bring to a boil over high heat. Reduce the heat to medium and simmer until the potatoes are tender and fall apart when pierced with a fork, about 30 minutes.

Drain the potatoes, reserving one and a half cups of the cooking liquid. Return the potatoes and reserved liquid to the pot and add the oil and spices. Mash with a potato masher. The potatoes might look liquidy at first, but they will absorb the liquid as you continue to mash, turning fluffy and moist.