Preparation Preheat oven to 350°F. Sift flour, baking soda, and salt into medium bowl. Using electric mixer, beat butter and vegetable shortening in large bowl until fluffy. Add sugar, brown sugar, sour cream, and vanilla and beat to blend well. Beat in eggs 1 at a time, then flour mixture. Stir in chocolate chips. Drop half of batter by generous 1/4 cupfuls onto 2 large ungreased baking sheets (5 mounds per sheet, spaced 3 inches apart). Using moistened fingertips, flatten each mound to 2 1/2-inch round. Bake cookies until golden brown, about 14 minutes. Cool on sheets 5 minutes. Transfer cookies to racks and cool completely. Repeat with remaining batter using cooled baking sheets.