In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add eggs, one at a time, mixing well after each addition; beat in vanilla. Continue to beat mixture 1-2 minutes until batter is pale in color. Add flour mixture to butter mixture in three additions, alternating with pumpkin and sour cream. Mix until just combined, scraping down bottom and sides of bowl as necessary. Pour into prepared pan, smoothing top of batter.