Place rhubarb in an ungreased 11x7-in. baking dish. Sprinkle with sugar; toss to coat. Cover and bake at 375° for 25-30 minutes or until tender, stirring occasionally. Cool slightly. Process in a food processor until blended. Transfer to a bowl; cover and refrigerate until chilled.
Stir in lemon juice. In a bowl, beat cream until stiff peaks form. Gradually fold into rhubarb mixture. Transfer to a shallow 1-qt. freezer container. Freeze, uncovered, for 1 hour, stirring every 15 minutes. Cover and freeze overnight.