Pit the cherries and discard the stones. Blend the pitted cherries in a food processor or blender until relatively smooth (smaller chunks are fine).
Separately, whip the cream until it forms medium-firm peaks.
Carefully fold the cherry puree and sweetened condensed milk into the cream so that it is combined (no white streaks) but without loosing too much air.
Pour the mixture into a plastic container or loaf tin, cover and transfer to the freezer. Leave to freeze for around an hour, then stir the mixture with a fork to mix through any chunks of cherry that may have fallen to the bottom (but without stirring so much you loose the air).
Re-cover and freeze for a further 3 hours, minimum, for soft-serve or ideally overnight.