This rich, cheesy potato dish is like "gossamer" Martha says. Chef David Bouley shared his recipe for this traditional French dish.
Place potatoes in a large saucepan and add enough water to cover; generously salt water and bring to a boil, adjusting the heat so that the water is bubbling, but not too rapidly. Cook until potatoes are tender, about 20 minutes.
Drain and mash or pass potatoes through a ricer into saucepan. Place over low heat and add milk; stir to combine. Add butter and stir until melted. Beat with a wooden spoon until stringy.
Remove from heat and stir in cheeses until melted; season with salt and pepper. Transfer to a bowl and drizzle with truffle oil. Serve with toasts.