In large bowl, beat 2/3 cup softened butter and the granulated sugar with electric mixer on medium speed, scraping bowl occasionally, about 1 minute or until fluffy. Beat in eggs, one at a time, until smooth. Stir in 1 1/2 teaspoons vanilla. Gradually beat flour mixture into sugar mixture alternately with buttermilk on low speed, beating after each addition, just until smooth. Scrape side of bowl occasionally.