125g unsalted butter, chopped, softened, plus extra 50g, chopped, softened
1 tsp vanilla bean paste, plus extra 1 tsp
2⁄3cup caster sugar
1 free-range egg
2 cups self-raising flour
2 cups icing sugar mixture
40ml iced water
½ cup raspberry jam
Put butter and vanilla in a large bowl and beat on high, using an electric hand mixer, for 1 minute or until smooth. Add caster sugar and beat for 1 minute or until pale and fluffy. Add egg and beat for 30 seconds or until combined. Sift in flour and mix until almost combined.
Form dough into a smooth ball. Divide in 2 and shape into discs. Wrap each in plastic wrap and chill for 30 minutes.
Preheat oven to 160°C fan-forced (180°C conventional). Line 4 oven trays with baking paper. Roll out each disc between 2 sheets of baking paper until 3mm thick. Use a 5cm fluted cookie cutter to cut 54 rounds, rerolling as necessary.
Arrange rounds on prepared trays, about 3cm apart. Bake, 2 trays at a time, for 12 minutes or until golden and firm to touch. Set aside on trays to cool completely.
Meanwhile, put extra butter and vanilla in a large bowl and beat, using an electric hand mixer, for 30 seconds. Add icing sugar and 1 tsp of water. Beat on low until sugar is incorporated. Increase to high and beat, adding remaining water, 1 tsp at a time, for 5 minutes or until pale, fluffy and glossy. Refrigerate uncovered for 15 minutes to firm slightly. 6 Spread 1 tsp of jam on base of 27 biscuits. Spread 1 Tbsp of buttercream on base of remaining biscuits and sandwich. Sandwiched biscuits will keep in an airtight container for 2 days (will soften slightly).