Add the potatoes and garlic to a large pot of salted water. Simmer over medium heat. Cook the potatoes until tender, about 15 minutes.
Reserve about a cup of the cooking water. I like to dip a coffee mug into the pot to collect the liquid. Then drain the cooked potatoes and garlic.
Return the drained potatoes and garlic to the pot. Using a potato masher, start mashing the potatoes and garlic.
Pour in the olive oil. Continue to mash, adding a little of the reserved cooking water at a time, as needed, to thin out the potatoes.
Season to taste with salt and pepper, and continue to mash until you reach your desired consistency of the potatoes.
Transfer to a serving bowl and top with minced chives, if using.
Cover and store any leftover olive oil mashed potatoes in the refrigerator for up to 3 days.Leftover mashed potatoes can be reheated in the oven in a covered baking dish at 350 degrees until heated through. Or cover and reheat in the microwave.