Place Yukon Golds into a pot with enough salted water to completely submerge. Heat to right below a simmer and cook until easily pierced with a fork.
In a small saucepot, bring the cream, butter and thyme to a simmer. Reserve warm.
Drain water and peel potatoes using a knife. Transfer to a food mill and pass through the mill back into a pot. Strain infused dairy into the potatoes and fold together over low heat. Season with salt.
Turn the heat up to medium and add the cheese. Stir constantly until the cheese melts.
Transfer to a serving tray and top with minced chives and sliced rounds of the truffle butter.
BLACK TRUFFLE BUTTER
Fold all ingredients together until thoroughly combined.
Lay out an 18- by 12-inch sheet of plastic wrap. Transfer the compound butter to the plastic wrap. Fold the plastic wrap over the butter. Create a cylinder with the butter and roll it until it forms a log. Transfer to the refrigerator until fully set (1 hour).