Preheat oven to 450°F (230°C). Mix the cherries and the sugar in a deep pan. Roast for 40 minutes, stirring occasionally. By the end, the cherries should be soft and wilted. Set them aside to cool.
Once the cherries are cool enough to handle, separate the stones from the flesh. The stones should pop out easily when you squeeze the cherries.
Add the cherry stones and the cream to a saucepan. Bring the cream to a simmer on the stove. Then remove from the heat, cover, and leave to cool down.
Blend the cherry flesh in a food processor. Depending on your food processor you may then need to strain the puree through a sieve to get rid of any bits.
Remove the cherry stones from the cream. Add 282g of the cherry puree to the cream. Then add the salt and the lemon juice. And give it another go in the food processor until well mixed and smooth.
Transfer the mixture to a vessel with a lid and refrigerate until around 42°F (6°C).
Add the mixture to your ice cream maker and churn it until it has the consistency of whipped cream. This usually takes between 15 and 30 minutes. Transfer to a plastic freezer box and freeze for at least an hour.
After an hour it should just be firm enough to serve without it melting too quickly. If you leave it longer and it's too hard to scoop, leave it in the fridge for a while to soften slightly.