Combine half of the melon pulp, the lemon juice and sugar in a saucepan. Heat until it reaches 50C (122F), stirring all the time.
Remove from heat and let cool down. Add the remaining melon pulp and the milk powder. Mix.
Strain the mixture and refrigerate until cold (about one hour).
Place the mixture in your ice maker for 25 minutes (or follow the manufacturer’s instructions).
Transfer to a container and place in the freezer for at least 2 hours before serving.