Ember-Roasted Corn and Leeks

Build a fire in a pit and let it burn down until coals are covered with ash. Rake a layer of coals away to one side of fire. Place 4 ears of corn, in husks, and 2 leeks on top. Roast, turning often, and adding more hot coals as needed, until husks are charred and peel back easily and leeks are starting to collapse, 15–20 minutes. Let cool slightly. Shuck corn. Trim roots from leeks; halve lengthwise. Remove tender inner flesh; discard charred layers. Spread vegetables with unsalted butter and sprinkle with flaky sea salt.