Cut all the potatoes into 3-inch pieces. Peel the garlic cloves and cut them in half.
Fill a medium-sized pan with water and boil all the potatoes. Add salt on the top. Cover the pan with a lid.
Usually, you would have to leave the potatoes for around 15-20 minutes, but before taking them off the heat, make sure that they can be easily pierced with a fork
Drain all the water off from the potatoes.
In the same pan, you can mash the potatoes (and also garlic) with a wooden masher. After that, add the butter and let it melt.
Add the liquid ingredients – the heavy cream, milk, and olive oil. Add more salt if it's necessary.
Then whip everything with a whisk for around 5 minutes or until is mixed everything evenly.
Finally, you can serve it with gravy if you wish. Enjoy!