Cream butter; gradually add 1/2 cup sugar, beating well at medium speed of an electric mixer.
Add egg, beating well.
Combine flour and baking powder; add to creamed mixture, and mix just until blended.
Stir in 1 teaspoon vanilla.
Pour into a greased 9-inch springform pan. Sprinkle with berries.
Combine sour cream and next 3 ingredients; pour over blueberries.
Bake at 350° for 1 hour or until edges are lightly browned. Cool on a wire rack; cover and chill.
To serve, remove cake from pan, and place on a serving plate.
Beat whipping cream until foamy; gradually add sugar, beating until soft peaks form.
Spoon half of whipped cream over top of cake.
Spoon remaining cream into a decorating bag with metal tip number 2110. Pipe a border around top. Garnish, if desired.