Wash the rhubarb well and chop crosswise into ½-inch pieces. Place in a medium-sized saucepan with the sugar and pinch of salt. Add a few tablespoons of water and bring mixture to a boil over medium-high heat, then reduce to a simmer. Cook rhubarb until soft and fragrant, stirring frequently, for about 10 minutes. Remove pot from heat and let cool slightly.

Purée rhubarb mixture in a blender on high speed to a smooth consistency, making sure to place a towel over blender lid. Taste for sweetness and adjust as needed. Pour through a fine-mesh strainer into a mixing bowl set over ice. Cool rhubarb purée completely over ice bath for at least 2 hours or refrigerate overnight. Once it’s cold, add rosewater and mix well. Freeze mixture in an ice cream machine according to the manufacturer’s instructions. Transfer to an airtight storage container and freeze at least 2 hours before serving.