Place sweet potatoes in a large saucepan with enough water to cover by one inch. Bring to a boil and cook until tender, about 30 minutes. Drain and set aside until cool enough to handle.
While potatoes are cooking, mix butter and brown sugar in a small saucepan. Bring to a boil and cook about 3 minutes, until sugar is dissolved and mixture is smooth. Stir in ginger, salt, and nutmeg; cook 2 minutes more, stirring occasionally.
Heat oven to 450°F. Peel cooled sweet potatoes and cut into 1/2-inch-thick slices. Butter a 9 x 13-inch baking dish. Place sweet-potato slices in rows in baking dish. Arrange pear cubes between rows. Pour syrup over pears and potatoes. Cover with aluminum foil and bake 10 minutes; uncover and bake 10 minutes more.