If you're peeling your potatoes, do so now. I peeled mine, but if you like more texture to your mashed potatoes, you can leave some, or all, of the skins on, just be sure to wash the potatoes really well.
Chop into small (roughly 1 inch) cubes and add to a large pot. Fill with 8 cups of water and 1 tablespoon of salt. I know that sounds like a lot of salt, but it's key for flavor and some of it will be drained with the water.
I used this herb infuser for the rosemary, but you can also wrap it in a cheesecloth. Either way, place that right into the pot and bring to a boil. Let simmer for about 15-20 minutes, or until the potatoes are fork tender.
Drain the potatoes but leave the colander in the sink for now.
Mince the garlic and add to the pot with 1 tbsp of oil. Saute until it just starts to brown, then remove from the heat and add the potatoes back in.
Use a potato masher to roughly mash, then add in the milk, olive oil, salt and pepper. Start with 1/2 cup of the milk and add more if you don't want a thick consistency.
Use a handheld electric mixer to beat just until creamy. Careful not to over do it or the potatoes can become gummy.
Taste and adjust flavors as desired, I usually add a touch more olive oil for a richer flavor and more salt and pepper.
Garnish with the chopped chives and enjoy!