In a bowl, combine flour, sugar, baking powder & salt. Cut in shortening & butter until crumbly. Add sour cream & blend until ball forms. Roll out on a floured surface into a 15″ x 10″ rectangle. Spread with 1/4 cup softened butter, sprinkle with remaining filling ingredients. Roll up, jelly-roll style, starting with the long side. Cut into 10 slices. Place slices, cut side down, in a 13″ x 9″ baking pan.