Step 1

Blend the custard powder, sugar and 2 tbsp of milk in a bowl, to make a smooth paste. Pour the rest of the milk into a pan and heat until almost boiling, then gradually pour the warm milk on to the custard paste, stirring all the time.

Step 2

Pour it back into pan and boil slowly for 1-2 mins. Take off the heat. Cool for 5 mins, then stir in the cream, vanilla and condensed milk. Cool. Pour into a plastic container and freeze until half-frozen. This will take about 1½ hours. Take out of the freezer and transfer to a large, chilled bowl. Beat until smooth, using electric beaters.

Step 3

Add the melon purée, whisk again and put into a plastic container and freeze. It will keep for 3 months.

Step 4

To serve: Remove from freezer about 15 mins before serving and use an ice-cream scoop to make scoops. Serve in sundae glasses.