Preparation Cook squash, 1 at a time, on high in microwave until very tender, turning once, about 25 minutes per side. Transfer to work surface. Cut in half lengthwise. Scoop out and discard seeds and fibers. Spoon all squash flesh into large bowl. Mash with potato masher. Transfer squash to large plastic or stainless steel strainer. Set strainer over same bowl. Cover; chill at least 1 day and up to 2 days while draining. Pierce sweet potato all over. Microwave on high until tender, 5 to 6 minutes per side. Cut potato in half lengthwise. Scoop flesh into medium bowl and mash. Measure 5 1/2 cups squash into large pot. Whisk in 1 cup mashed sweet potato, then chicken fat and allspice. Stir over medium heat until hot. Season to taste with coarse salt and pepper.
Preparation Cook squash, 1 at a time, on high in microwave until very tender, turning once, about 25 minutes per side. Transfer to work surface. Cut in half lengthwise. Scoop out and discard seeds and fibers. Spoon all squash flesh into large bowl. Mash with potato masher. Transfer squash to large plastic or stainless steel strainer. Set strainer over same bowl. Cover; chill at least 1 day and up to 2 days while draining. Pierce sweet potato all over. Microwave on high until tender, 5 to 6 minutes per side. Cut potato in half lengthwise. Scoop flesh into medium bowl and mash. Measure 5 1/2 cups squash into large pot. Whisk in 1 cup mashed sweet potato, then chicken fat and allspice. Stir over medium heat until hot. Season to taste with coarse salt and pepper.