Twice-Baked Potatoes with Porcini & White Truffles

• 1/4 oz. dried porcini mushrooms (about 1/4 cup)
• 4 medium russet potatoes (about 8 ounces each), scrubbed
• 3-1/2 Tbs. unsalted butter, at room temperature
• 1/2 cup crème fraîche or sour cream, at room temperature
• 1/4 cup half-and-half, warmed
• 1/2 to 1 tsp. white truffl e oil
• 3/4 tsp. kosher salt
• Freshly ground white pepper

Position a rack in the center of the oven and heat the oven to 350°F. Set the potatoes directly on the oven rack and bake until tender all the way through, 1 hour to 1 hour and 15 minutes. Transfer the potatoes to a work surface and let them cool for 10 to 15 minutes.

While the potatoes are baking, soak the mushrooms in 1 cup very hot water. Drain the mushrooms, saving the liquid for another use (such as a soup, stock, or sauce). Finely chop the mushrooms.

Examine each potato to see if there’s a way to halve it to give you two shallow, wide halves rather than taller, narrower ones. With a large chef's knife, slice each potato in half lengthwise, cutting cleanly— not sawing—so as not to tear the skin. Using a dishtowel or oven mitt to protect your hand from the heat, hold a potato half in one hand and gently scoop out the flesh with a spoon, leaving the shells 1/4 to 1/8 inch thick.Repeat with the remaining halves. Force all the flesh through a potato ricer or mash it with a potato masher; transfer it to a mixing bowl.

With a wooden spoon, stir 3 Tbs. of the butter, the crème fraîche, half-and-half, chopped mushrooms, 1/2 tsp. of the truffle oil, the salt, and pepper to taste into the mashed potato flesh. Taste and add more truffle oil, if you like. Scoop the filling into the potato skins, compacting it lightly. For a rough-textured surface, mark it with the tines of a fork. Top each with bits of the remaining 1/2 Tbs. butter.

Heat the oven to 400°F. Arrange the potatoes on a baking sheet or in a large baking dish. Bake until heated through and beginning to brown in spots on top, 25 to 30 minutes (or 35 to 40 minutes if made ahead and refrigerated). Let sit for about 10 minutes before serving.