In large bowl, beat 1/2 cup softened butter and the granulated sugar with electric mixer on low speed 30 seconds; increase speed to high, and beat 3 to 4 minutes or until light and fluffy, scraping bowl occasionally. Reduce speed to low; beat in eggs, one at a time, just until smooth. Beat in 1 teaspoon vanilla. On low speed, beat in one-third of the flour mixture, then half of the milk, beating well after each addition, just until smooth. Repeat with flour mixture and milk, ending with flour mixture. Scrape side of bowl occasionally. Beat in sour cream until blended. Stir in toffee bits. Pour in pan.