Boil rhubarb, sugar, water, and orange juice in a pan and simmer for 10 minutes.
Strain the mixture through muslin and a sieve, reserving both liquid and pulp.
Measure the juice volume and set the pulp aside.
Soak the required number of gelatine leaves in water until soft.
Heat the juice gently and whisk in the squeezed gelatine until dissolved.
Pour half the liquid into four 150ml moulds and chill until set.
Top with reserved pulp, add remaining liquid, and chill again until fully set.
Preheat the oven to 180°C.
Mix icing sugar, flour, cornflour, and almonds, then rub in the butter.
Knead the mixture on a floured surface into a smooth dough.
Roll dough to 4mm thick, cut into 5cm discs, and bake for 12 minutes.
Unmould jellies and serve with shortbread layered with ice cream and icing sugar.