Mix the cream cheese, sour cream, corn starch and sugar with an electric mixer. Add the butter and vanilla, blend until smooth. Pour into the prepared graham cracker crust and dot the top with Aroniaberry Concentrate. Swirl with a knife to create a marble effect and bake @ 350 for 25 minutes or until a knife inserted comes out almost clean. Cool and chill for at least one hour. Cut into small squares and serve.