Truffled Potatoes Au Gratin Recipe
Active time: 45 minutes
Total time: 1¾ hours
In a large high-sided skillet or a large, wide pot, melt butter over medium heat. Add shallots and cook, stirring often, until softened and translucent, about 2 minutes. Stir in flour. Whisk in milk until smooth. Stir in cream, salt, pepper, and nutmeg. Add potatoes and gently stir to combine. (The liquid should just cover the potatoes.)
Cover surface with a circle of parchment paper cut as wide as the pot. Bring just to a boil, reduce heat to medium-low, and simmer, carefully lifting parchment and gently stirring halfway through, until potatoes are just tender when pierced with a fork, about 20 minutes.
Meanwhile, preheat oven to 450° and lightly butter a 9" x 13" casserole dish. Carefully pour half the potato mixture into the prepared dish and arrange Gouda in a single layer over the top. Cover evenly with remaining potato mixture. Finely grate Parmesan directly over the potatoes and bake until bubbly and golden brown, about 15 minutes. Set aside to let rest for 20 minutes before serving. (The liquid will thicken as it cools.)