Put the potatoes in a pot and cover with cold water. Put the pot over medium-high heat and cook until the potatoes are fork tender, about 15 to 20 minutes. Drain, return to the pot and put over low heat for 3 minutes to dry the potatoes. Mash them with a potato masher.
While the potatoes are boiling combine the cream, butter, sour cream, and rosemary and thyme sprigs in a pot over medium-low heat. Heat to a simmer, turn off the heat and let steep 10 minutes. Remove the herb sprigs and discard. Slowly add the heated cream and butter to the potatoes and mix in with a wooden spoon or a hand mixer until all the cream is incorporated. Be careful not to overmix or the potatoes will become gummy.