*NOTE: Do not use freshly ground or "old-fashioned style" peanut butter. Butterfinger bars should be cut into 1/2-inch pieces. Preheat oven to 350F. Lightly grease 2 cookie sheets. STEEL KNIFE:(Food Processor recipe) Blend sugars, butter, egg whites and vanilla until fluffy, stopping once to scrape down sides of work bowl, about 1 minute. Add peanut butter and process until combined, about 20 seconds. Add flour, baking soda and salt and blend until just combined using 2 to 3 on/off turns; do not overprocess. Transfer to large bowl. Stir in chopped Butterfingers. Mound dough by 1 1/2 tablespoonfuls onto prepared sheets, spacing 2 inches apart. Flatten slightly using fingers. Bake until dry in appearance and centers are still slightly soft to touch, about 15 minutes. Cool on cookie sheets 3 minutes. Transfer to rack and cool completely. Store in airtight container. (Can be prepared ahead. Store 4 days at room temperature or freeze 3 weeks.)