Method

• 1.
  To make rosella jelly, line a 3-cup (750ml) rectangular container with plastic wrap, leaving plenty overhanging. Soak gelatine in a bowl of cold water for 5 minutes to soften. Whiz 2 jars rosella flowers and syrup in a food processor for 2 minutes, or until smooth.

• 2.
  Transfer puree with 1 cup (250ml) water to a pan over medium heat and bring to a simmer. Squeeze excess liquid from gelatine and add to pan.
• 3.
  Cook, stirring, until melted and combined. Pour into the container and set aside to cool. Cover with overhanging plastic wrap and chill overnight to set.
• 4.
  The next day, to make vermouth syrup, place sugar, bay and vermouth in a small saucepan over medium heat, stirring until sugar dissolves.
• 5.
  Bring to the boil, then reduce heat to low and simmer for 10 minutes, or until reduced and thickened. Set aside to cool.
• 6.
  To make the sponge, preheat oven to 180°C/160°C fan-forced. Grease and line a 20cm round cake pan with baking paper. Combine the flour and baking powder in a bowl.
• 7.
  Using a stand mixer, whisk the eggs and sugar for 5 minutes or until tripled in size. Working quickly, add our mixture and whisk to combine. Add melted butter and briefly whisk to combine. Immediately pour batter into cake pan and bake for 20 minutes.
• 8.
  Reduce oven to 160°C/140°C fan-forced and bake for a further 25 minutes, or until firm to the touch. Remove from oven and cool cake completely in pan set on a wire rack.
• 9.
  For the custard, toast vanilla beans in a dry pan over high heat for 4 minutes or until fragrant. Remove from pan and cool slightly. Place milk and cream in a heavy-based saucepan.
• 10.
  Slice vanilla beans in half lengthways and scrape out seeds. Add seeds and pods to milk mixture and place pan over medium heat. Bring to the boil, then remove from heat. Whisk cornflour, egg yolks and sugar in a heatproof bowl until thick and pale.
• 11.
  Pour milk mixture over egg mixture and whisk until combined. Return mixture to pan and place over medium heat. Cook, stirring, for 10-12 minutes, until thickened. Strain into a heatproof bowl, discarding vanilla pods. Cover with plastic wrap touching the surface, to stop a skin forming.
• 12.
  Cool custard to room temperature, then chill for 1 hour, or until thickened and cooled. Using a stand mixer, whisk mascarpone to loosen. Whisk in cooled custard until thick. Chill for 1 hour or until thickened.
• 13.
  Cut sponge and jelly into 3cm pieces. To assemble trifle, place half the jelly in a 2.5L (10-cup capacity) glass trifle bowl. Top with half the sponge, drizzle over half the syrup (reserving 1 tbs), then spoon over half the custard. Repeat, finishing with reserved 1 tbs syrup and remaining 1 jar rosella flowers.