In large bowl, beat granulated sugar, 1 cup butter, vanilla and eggs with electric mixer on low speed 30 seconds. Beat on high speed 5 minutes, scraping bowl occasionally. Beat flour mixture into sugar mixture alternately with milk mixture on low speed, beating just until smooth after each addition. Spread 3 cups batter into pan. Sprinkle streusel mixture over batter. Carefully spread remaining batter over streusel.