In a 5- or 6-quart Dutch oven cook squash in lightly salted boiling water, covered, for 16 to 17 minutes or until tender when pierced with a fork. Drain.
Meanwhile, melt the butter in a heavy skillet over medium heat, whisking frequently until golden brown, 5 to 6 minutes. Transfer half the squash mixture to a food processor. Add butter, sour cream, maple syrup, orange and lemon peels, salt and pepper. Cover and process until smooth. Place remaining squash in a bowl; add pureed mixture. Mash slightly. Stir in fresh sage.
Top with pecans, green onions and/or sage leaves, and additional citrus peel.