Line an 18cm high-sided springform cake tin with baking paper, allowing the paper lining the sides to sit about 10cm above the tin.
Make both jellies according to packet instructions and set in shallow tubs or trays. Once set, cut into 1.5cm cubes. You probably won’t need all of it. Drain peaches and cut each slice into 2-3 pieces.
Cut each sponge horizontally in half. You will need three of the four rounds.
Place ¼ cup warm water in a small bowl and sprinkle over gelatine. Place bowl in a large dish filled partway with boiling water and stir gelatine until dissolved.
Use electric beaters to whip cream until thick. Set aside ⅓ of the whipped cream. Add custard to remaining cream and beat to combine. Add dissolved gelatine and continue beating until smooth and thick.
Place one cake half in the base of the prepared tin. Pour in one-quarter of the custard mixture. Top with jelly cubes and peach slices. Spoon over another quarter of the custard mixture and smooth the top. Add a second cake half. Repeat with remaining custard mixture, including more jelly cubes and peaches in the mix. Finish with a third half of sponge cake (choose one of the top halves for a smooth rounded finish). Wrap in cling film, ensuring the cake that is hovering above the tin is being held firmly in place. Refrigerate for 4 hours to set.
When you are ready to serve, carefully unwrap the cake and unclip the springform tin. Gently slide the cake onto a serving stand and unpeel the baking paper.
Place reserved whipped cream in a piping bag with a rosette tip and pipe 10 cream puffs on top of the cake. Top each with a maraschino cherry.
