1.Preheat oven to 200°C (180°C fan forced). Grease oven trays, line with baking paper.
2.Dissolve coffee granules in the water in a small jug.
3.Beat butter, sugar and egg in a small bowl with an electric mixer until light and fluffy. Beat in sifted flours, cocoa and soda, buttermilk and coffee mixture, on low speed, until mixture is smooth.
4.Drop level tablespoons of mixture about 5cm (2 inches) apart onto trays.
5.Bake pies about 10 minutes. Cool on trays.
6.Meanwhile, make vanilla cream cheese filling. Beat cream cheese, sugar and vanilla bean paste in a small bowl with an electric mixer until smooth. Beat in cream.
7.Spoon filling into a piping bag fitted with a 2cm (¾-inch) fluted tube. Pipe filling on flat side of half of cooled pies, sandwich with remaining pies.
8.Serve dusted with dark cocoa powder.
Whoopie pies are best eaten the day they are made.Note