In a large stock pot fill with enough water to cover potatoes once they are peeled and cubed.
Bring to a boil over high heat, once boiling add 2 tablespoons kosher salt, be careful as this will make the water boil very rapidly for a few seconds.
Peel and cut the potatoes into equal sized pieces, quartering them is perfect.
Add the cut potatoes and the garlic cloves to the boiling water and cook until the potatoes are soft and easily pierced all the way through with a knife.
While the potatoes are cooking use a small sauce pan to melt the butter with the cream and milk. Bring the mixture to a simmer being careful not to boil over.
Strain the potatoes and garlic through a colander in the sink. Let sit for a few minutes to cool and dry out and wipe the pot out to remove any large pieces that may have stuck to the sides or bottom. Using a ricer press the potatoes and garlic cloves through and back into the pot that you boiled the potatoes in. Once all the potatoes are mashed add the package of the garlic and herb boursin cheese and half of the butter, cream milk mixture. Gently mix with a rubber spatula or large spoon to incorporate with cheese and butter mixture. Scrape from the side of the pot and fold the potatoes back over into the middle. Add more of the warm butter and milk mixture until the desired consistency is reached in the mashed potatoes. Add salt and pepper to taste.
Transfer to the baking dish and cover with foil.
At this point you can refrigerate for up to two days before serving. To reheat the potatoes if they have been refrigerated let them come to room temperature for at least 2 hours before reheating. Place them covered in foil into a 350 degree oven and heat for 30-45 minutes or until a knife is inserted into the middle of the potatoes and hot to the touch on your lip, be careful not to burn yourself! Sometimes the potatoes will bubble over the side of the baking dish while reheating, you may want to have the dish on a sheet tray while in the oven to catch the spillage.