Preheat the oven to 375˚ F. Line a half-sheet pan with foil. Put 3 large sweet potatoes on the pan and bake until very soft, 1 to 1 1/2 hours. Whisk 1/2 cup packed brown sugar, 1/4 cup extra-virgin olive oil, 2 tablespoons molasses, the zest and juice of 1 clementine and 1 teaspoon kosher salt in a large bowl. Peel the potatoes and pass through a food mill or ricer into the bowl. Fold until well mixed. Divide among 4 cups, sprinkle with flaky salt and serve hot or warm.