|Heat oven to 350 degree. Beat all ingredients except chocolate chips in large bowl on high speed, scrapping bowl occasionally, until fluffy, about 1 minute. (Do not use blender.)|
Pour mixture into ungreased pie plate and bake until puffed and dry in center and knife inserted in center comes out clean, about 35 minutes; cool slightly. Heat chocolate chips in a 1-quart saucepan over low heat, stirring occasionally, until melted. Spread chocolate over pie. Sprinkle with chopped peanuts if desired. Refrigerate until chocolate is firm, about 1 hour.
In high altitude (3,5900 to 6,500 feet), decrease brown sugar to 3/4 cup. Bake about 40 minutes.