Heat oven to 375°F. In large bowl, beat brown sugar, butter and egg with electric mixer on medium speed, or mix with spoon. Stir in flour, baking soda and salt (dough will be soft). Stir in nuts, 4 ounces bittersweet chocolate, 4 ounces sweet chocolate and 4 ounces white chocolate. Drop dough by rounded tablespoonfuls about 2 inches apart onto ungreased cookie sheet.