1. Place first 4 ingredients in a large bowl; beat with a mixer at high speed 2 minutes until well blended. Add egg and egg white, one at a time, beating well after each addition.
2. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking powder, and salt in a small bowl, stirring well with a whisk. Add flour mixture to sugar mixture, stirring until blended. Stir in 1/4 cup chips and pecans (dough will be sticky). Cover and chill 30 minutes.
3. Preheat oven to 325°.
4. Turn dough out onto a heavily floured surface. With floured hands, shape dough into a 9 x 4–inch log; pat to 1/2-inch thickness. Place log on a baking sheet coated with cooking spray. Bake at 325° for 30 minutes. Remove log from pan; cool 10 minutes on a wire rack. Cut log crosswise into 18 (1/2-inch-thick) slices. Place, cut sides down, on baking sheet. Bake at 325° for 15 minutes or until lightly browned. Cool completely on wire rack.
5. Place remaining 1/4 cup white chocolate chips in a glass measure; microwave at HIGH 30 seconds or just until melted. Add fat-free half-and-half; stir until smooth. Drizzle over biscotti.