Preheat oven to 350°F (180°C). In medium bowl, whisk together all-purpose flour, whole-wheat flour, baking soda and salt. In large bowl, with electric hand mixer beat the butter with both sugars until light and fluffy. Beat in egg and vanilla. Stir in flour mixture until combined. Fold in chocolate chips and walnuts (if using).
Place heaped tablespoons of batter 2 in. (5 cm) apart on parchment-lined baking sheets. Bake batches 12 min., or until tops are set and bottoms are golden brown, switching sheets to other oven racks and rotating half-way through baking for even cooking.
Cool on baking sheet 2 min. Transfer to wire rack to cool completely. Store in airtight container up to 2 days or freeze up to 2 weeks.
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