Step 1Cut the potatoes into large, even chunks and place in a pot with water to cover. Add a tablespoon or so of salt. Bring to a boil and cook until the potatoes are soft, about 25 minutes.
Step 2While the potatoes cook, melt the butter in a small saucepan and add the cream; stir until heated. Set aside.
Step 3Drain the potatoes well and transfer to a large bowl. Add the butter mixture and mash partway. Add the creme fraiche and continue mashing until completely smooth. Season with salt and pepper. Divide among serving trays and drizzle with truffle oil to taste.