Peel the melon from its hard skin and chop it into 2.5 cm pieces. Place in a zip plastic bag in one layer and freeze.
Pour the elderflower cordial, maple syrup, water, lemon juice with half of the fresh lemon leaves into a small pot. Bring to the boil and then simmer for 5 minutes.
Take it off the heat and let cool down and infuse. When it's cool, strain it through a sieve, discarding the mint.
Place the frozen melon pieces, the cooled syrup and the rest of the fresh mint into a food processor. Blend into a smooth consistency. Serve straightaway. You can also place the rest in a freezable container. Just remember to take it out of the freezer 10 minutes earlier to soften up a bit before serving.