Cream together sugar and butter, add eggs and beat well. Combine flour, baking powder, soda, salt and alternatively with yogurt. When well blended, add saskatoons and stir gently. Spoon half of the mixture into a well greased pan (bundt, ring mold or 9″ sq), sprinkle with nut mixture and top with remaining batter. Bake at 350 F for 40-45 mins. When slightly cool, sprinkle with icing sugar and lemon rind if desired.