Lightly grease a 27½ x 17½cm (3½ cmm deep) slice pan, then line with baking paper

Break biscuits into a food processor and process until fine crumbs form. Add 150g melted butter, processing to combine. Using the back of a spoon, firmly press mixture evenly into base of pan, then refrigerate.

Meanwhile, place lemon and lime zest and juice, sugar and egg in a saucepan, whisking to combine. Place gelatine and 1 tbs warm water in a small bowl, mixing to combine. Place saucepan over low heat and cook, whisking constantly for 5 minutes or until mixture is a custard consistency. Remove pan from heat and add gelatine mixture, stirring to dissolve. Add remaining chopped butter and stir until combined.

Remove pan from fridge. Carefully pour curd through a sieve over biscuit base, then return pan to fridge.

To make the jelly, place bitters, lemonade and sugar in a small saucepan and bring to the boil over low heat. Meanwhile, place gelatine and 2 tbs warm water in a small bowl, mixing to combine. Remove pan from heat and add gelatine mixture, stirring to dissolve. Cool completely, then transfer mixture to a jug. Pour jelly over curd layer. return slice pan to fridge and chill for at lest 4 hours or until set. Slice and serve topped with extra lime slices.