In large bowl, beat softened butter and brown sugar with electric mixer on medium speed until light and fluffy, scraping bowl occasionally. Beat in vanilla and eggs until well blended. On low speed, beat in flour and baking soda until well combined, scraping bowl occasionally. Dough will be soft. Divide dough into 4 pieces; flatten each piece, and wrap in plastic wrap. Refrigerate about 3 hours or until dough is firm and cold.