Place potatoes and a dash of salt in a medium saucepan. Cover with water and bring to a boil. Reduce heat to low, cover, and simmer for 15 minutes or under tender. Cool slightly.
Transfer potatoes to large bowl and mash. Stir in milk, butter, truffle oil, salt, and pepper.
Put mashed potatoes in a gratin dish or individual ramekins. In a small bowl, combine olive oil, panko, and cheese; stir until well-coated.
Top mashed potatoes with panko mixture. Bake for 20 minutes or until panko mixture is golden brown.
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