Mince (chop) the garlic and rosemary leaves as finely as you can.
Add the oil to a pot or large skillet and put on a medium heat. Once warm, add the chopped garlic and rosemary.
Cook for 5 minutes, stirring occasionally, til the garlic and rosemary softens, but not browned.
Add the cream and butter to the garlic and rosemary, along with a few pinches of black pepper and about ¼ teaspoon of salt.
Bring the cream mixture to a boil, then take off of the heat and let the flavors infuse.
While the cream sits, peel the potatoes and chop into chunks. Place in a large pot of cold salted water. Bring to a boil and cook (for about 15-20 minutes)til fork tender.
Drain the potatoes and place back in the pot. Pour the infused cream over the potatoes and mash together.
Taste and adjust seasoning if needed.