In large bowl, beat butter, brown sugar and granulated sugar with electric mixer on medium speed until creamy. Add eggs, one at a time, beating on low speed after each addition until blended. Add pumpkin and 2 teaspoons vanilla; beat on medium speed until blended. On low speed, beat in flour mixture alternately with 1/2 cup milk until smooth. Stir in 1 cup of the chocolate chips. Spoon batter into pan.