BOIL rhubarb in a medium saucepan (without added water) over high until tender and all liquid has evaporated, about 10 min. Rhubarb should measure about 1/3 cup. Chill until rhubarb is completely cooled.
BEAT cream in a medium bowl, using an electric mixer on medium, until soft peaks form, 2 to 4 min. Reduce speed to low and beat in sweetened condensed milk and rhubarb until just combined. Mixture should be smooth and fluffy.
SCRAPE mixture into a resealable container. Freeze until firm, 6 hours.
Chatelaine Quickies: how to make 3-ingredient rhubarb ice cream