Cook over medium-high heat until mixture comes to a boil. Reduce heat to medium and cook for 10 – 15 minutes until cranberries all popped and soften, stirring occasionally.
Pour the cooked cranberries in a food mill over a large bowl to separate the cranberry puree from the skins and seeds. Rinse out and dry the saucepan.
Put the cranberry puree back in the saucepan and add the sugar and the liquid pectin. Bring to a boil over medium-high heat, stirring frequently. Boil one minute.
Allow mixture to cool slightly and then pour cranberry jelly into a bowl or a mold coated with nonstick cooking spray. Chill until set.
To unmold, dip mold in warm water for 5 seconds, then invert jelly onto serving platter.