Place 1 cup of the pistachios in food processor or clean coffee grinder; cover. Pulse until finely ground. Prepare cake mix as directed on package, adding 1 additional egg, ground pistachios and vanilla.
Bake as directed in 2 (9-inch) round cake pans. Cool in pans 10 minutes. Remove from pans cool completely on wire racks.
Meanwhile for the Raspberry Buttercream, beat butter and raspberry flavor in large bowl until light and fluffy. Gradually add confectioners' sugar, beating well after each addition and scraping sides and bottom of bowl frequently. Add milk; beat until light and fluffy. If frosting is too thick to spread, gradually beat in additional milk. Fill and frost cooled cake with Raspberry Buttercream. Garnish with remaining 1/2 cup pistachios and raspberries.