Preparation Adjust oven rack to lowest position and heat oven to 400°F. Place potatoes cut side down on a foil- or parchment-lined baking sheet. Bake until fork-tender, about 30 minutes. Let cool slightly. Holding a potato half with a pot holder, scoop potato flesh into a blender or food processor, leaving a 1/4-inch shell. Repeat with remaining potatoes; set shells aside. With motor running, gradually add both milks to potatoes. Add butter, then process, adding a little more milk if necessary, until potatoes are silky smooth. Add salt and pepper to taste. Spoon puree back into potato shells. Sprinkle marshmallows over potatoes. Place on baking sheet and bake until potatoes are hot and marshmallows are golden brown, 10 to 12 minutes. Serve hot.
Preparation Adjust oven rack to lowest position and heat oven to 400°F. Place potatoes cut side down on a foil- or parchment-lined baking sheet. Bake until fork-tender, about 30 minutes. Let cool slightly. Holding a potato half with a pot holder, scoop potato flesh into a blender or food processor, leaving a 1/4-inch shell. Repeat with remaining potatoes; set shells aside. With motor running, gradually add both milks to potatoes. Add butter, then process, adding a little more milk if necessary, until potatoes are silky smooth. Add salt and pepper to taste. Spoon puree back into potato shells. Sprinkle marshmallows over potatoes. Place on baking sheet and bake until potatoes are hot and marshmallows are golden brown, 10 to 12 minutes. Serve hot.