Grease spring form pan.
Sift flour, baking powder, soda and salt together.
Put eggs, shortening, sugar and vanilla into a blender and process at mix until smooth.
Push Blend button and gradually add half sour cream and half flour.
Process until smooth.
Repeat with remaining sour cream and flour.
Pour half the batter into prepared pan, top with half the topping mixture spread as evenly as possible.
Repeat with remaining batter and topping.
Bake 350°F 45-55 minutes or until done.
Cool 10 minutes before removing from pan.
Serve warm with butter.
