Step 1
Line a 12-hole (1/3 cup/80ml) muffin pan with paper cases. Use a small sharp knife to cut the thin brown surface from the sponge, if present. Using a 5.5cm cutter, cut 6 rounds from the sponge. Cut each round in half horizontally to make 12 rounds. Spread each round with jam. Place a round, jam-side-up, in each paper case. Sprinkle each with ½ tsp hundreds and thousands.
Step 2
Pour the custard into a jug. Place the gelatine leaves in a bowl and cover with cold water. Soak for 5 minutes or until soft. Squeeze excess water from the gelatine and place in a small saucepan. Stir over very low heat for about 15 seconds or until melted. Stir into the custard until evenly combined.
Step 3
Pour half the custard mixture over the sponge rounds. Sprinkle each with another ½ tsp hundreds and thousands, then pour the remaining custard over the top (the hundreds and thousands will move around, but don’t worry). Place in the fridge for 45 minutes or until just set.
Step 4
Meanwhile, place the jelly crystals in a heatproof jug. Add boiling water and stir until crystals dissolve. Stir in 80 ml (⅓ cup) cold water. Place in the fridge, stirring occasionally to cool evenly, for about 30 minutes or until cool but not chilled – you don’t want it to start to set.
Step 5
Evenly pour jelly mixture over the top of the custard layer in the paper cases. Place in the fridge for 3 hours or until set.
Step 6
Lift the trifle cakes out of the muffin pans. Gently pull paper cases around the edges to loosen and remove. Arrange cakes on a serving plate. Place whipped cream in a piping bag fitted with a 1cm nozzle. Pipe a small swirl of cream on top of each cake and sprinkle with extra hundreds and thousands. Serve straightaway (see notes).