Preparation Combine rhubarb pieces, sugar and fresh lemon juice in heavy large Dutch oven. Cover and refrigerate until juices form, stirring occasionally, at least 8 hours or overnight. Bring rhubarb mixture to simmer over medium heat, stirring until sugar dissolves. Increase heat to high and boil until rhubarb mixture thickens slightly, about 5 minutes. Add raspberries and boil until mixture is thick, stirring occasionally, about 6 minutes longer. Remove jam from heat. Stir in ground cardamom. Cool jam completely. (Jam can be made 1 week ahead. Store in covered container in refrigerator.)
Preparation Combine rhubarb pieces, sugar and fresh lemon juice in heavy large Dutch oven. Cover and refrigerate until juices form, stirring occasionally, at least 8 hours or overnight. Bring rhubarb mixture to simmer over medium heat, stirring until sugar dissolves. Increase heat to high and boil until rhubarb mixture thickens slightly, about 5 minutes. Add raspberries and boil until mixture is thick, stirring occasionally, about 6 minutes longer. Remove jam from heat. Stir in ground cardamom. Cool jam completely. (Jam can be made 1 week ahead. Store in covered container in refrigerator.)