Preheat oven to 300 degrees. Toast the pistachios in the oven until crisp, about 15 minutes. Do not let them brown. Rub them between your fingers to remove as much skin as possible. Grind the nuts finely. Butter and flour a 10 inch pan. Raise the oven to 350. Sift flour with baking soda, baking powder and salt. Beat egg yolks with half the sugar until pale and very thick. Mix in the yogurt and then the olive oil. Fold in the flour and nuts. Beat egg whites with cream of tartar to soft peaks. Add remaining sugar and beat to firm peaks. White should look shiny and not dry and granular. Gently fold egg whites into the batter. Pour into the pan and bake 55 minutes or until done. Cool on a rack.