Preheat oven to 170°C (150°C fan-forced). Line muffin pans (⅓-cup/80ml capacity) with paper cases.

Stir the butter, white chocolate, sugar and milk in a medium saucepan over low heat until smooth – do not let it boil. Transfer the mixture to a medium bowl; cool for 15 minutes.

Whisk sifted flours into white chocolate mixture, then add eggs and vanilla. Drop ¼ cups (60ml) of mixture into cases. Bake for about 25 minutes or until cooked when tested. Cool on wire racks.

Make ghost frosting: Combine sugar, water and cream of tartar in a medium saucepan; stir over low heat until the sugar dissolves. Bring to the boil; boil for 3-4 minutes or until syrupy.

In the medium bowl of an electric mixer, beat the egg whites until soft peaks form. Gradually pour in the hot syrup in a thin, steady stream, beating constantly, until thick and glossy. Continue beating until mixture cools to room temperature.

Spoon frosting into a large piping bag fitted with a 1.5cm plain nozzle. Pipe a swirl to resemble a ghost onto each cupcake. Position jellybeans onto each ghost to resemble eyes.