• Pre-heat oven to 180C/160C fan forced.

Shortbread biscuits

• For the biscuits, in a food processor, combine the butter, flour and salt until the mixture resembles fine breadcrumbs.
• Add the sugar and yuzu zest and whizz until combined and smelling fragrant.
• Add the yuzu juice, vanilla and egg yolk and whizz again until the mixture comes together in a large ball.
• Tip the dough out onto a lightly floured bench and knead briefly until it comes together in a smooth ball. Be careful not to overwork it otherwise it will be tough.
• Cut the dough into 2 halves and pat with your hands into flat discs. Wrap the discs in plastic film and chill in the fridge for at least 30 mins. Line 2 baking sheets with baking paper.
• Remove the dough from the fridge and allow to rest outside of the fridge for about 15 minutes or until it starts to feel pliable. Unwrap 1 piece of dough, lightly flour your bench and rolling pin and roll it out to be about 3mm thick. Using a 6cm round or flutted cookie cutter stamp out discs and transfer them to a baking sheet using a palette knife.
  
• Unwrap and roll out the other half of the dough to the same thickness. Stamp out the same size discs and transfer to the second baking sheet. Using a small round cutter about 1cm in diameter or the end of a large round piping nozzle stamp holes from the middle of 1/2 of the biscuits. Loosely cover the trays with plastic film and chill for 15 minutes in the refrigerator.
  
• Once the cookies are chilled, place them immediately in the pre-heated oven for 15 mins. You may need to turn and swap the trays over halfway through to get an even golden colour on all cookies. Remove from the oven, and leave to cool for 5 minutes before transferring them to a wire rack to cool completely.
• Meanwhile, make the fillings.

Yuzu Lemon Curd

• For the Yuzu Lemon Curd, bring a small saucepan of water to the boil and place a small glass bowl which snugly fits on top of the sauceplan to create a bain marie
• Place the yuzu and lemon juice, zest, butter salt and sugar in the glass bowl. Sit the bowl on top of the simmering pan and stir until the butter has melted.
• Add the egg and egg yolks to the bowl and continue stirring over a gentle heat for 10–12 minutes, or until the curd has thickened to a custard-like consistency. Refrigerate until cool. Don't worry if the curd seems a little runny as it will thicken up in the fridge.
• If you have a Themomix, you can place the sugar and zests into Thermomix bowl and mill 10 sec/speed 10. Add butter and mix 5 sec/speed 7. Then add remaining ingredients. Cook 10 min/80°C/speed 5. Finish cooking 2 min/90°C/speed 6.

Yuzu Lemon Buttercream

• For the Yuzu Lemon Buttercream, place the butter, vanilla, sugar and 50g of the lemon curd in a medium-sized bowl or stand mixer fitted with a paddle attachment and beat until thick and creamy. Transfer to a piping bag and snip off the end, making a 1cm opening. Place the remaining lemon curd in another piping bag and snip off the end to make a slightly smaller hole.

Lemon Sherbet

• For the Lemon Sherbet, Combine all ingredients well in a bowl and dust a little sherbet over the biscuits with a hole in the centre.
  

To assemble

• To assemble, pipe blobs of Yuzu Lemon Buttercream in a ring shape onto each whole biscuit, leaving space in the centre to fill with Yuzu lemon curd. Fill the middles with the curd, then sandwich a sherbet-dusted biscuit on top of each one.
  
• Serve immediately and try not to eat them all at once.