Remove stem from squash. Cut squash lengthwise into 4 pieces; remove and discard seeds. Cook squash in boiling water to cover in a large saucepan over medium-high heat 10 to 15 minutes or until tender. Drain well; let cool for 25 minutes or until completely cool. Remove and discard peel.
Process squash and eggs in food processor until smooth, stopping to scrape down sides. Add sour cream and remaining ingredients; process 20 to 30 seconds or until smooth. Pour mixture into a lightly greased 8-inch square baking dish. Bake at 350 degrees for 55 to 60 minutes or until set.