01 - Rinse cranberries under cold water and remove any stems or soft berries.
02 - In a medium saucepan, combine cranberries, water, and lemon zest if using.
03 - Bring mixture to a boil over medium-high heat, then reduce to a simmer. Cook for 10 minutes, stirring occasionally, until cranberries burst and soften.
04 - Remove and discard lemon zest from the saucepan.
05 - Strain the cooked cranberries through a fine mesh sieve into a bowl, pressing firmly to extract juice and pulp. Discard solids.
06 - Return strained liquid to the saucepan, add sugar and lemon juice if using.
07 - Bring to a boil while stirring constantly, then simmer for 8 to 10 minutes until thickened and jelly-like.
08 - Remove saucepan from heat and let cool for 5 minutes.
09 - Pour mixture into a serving dish or mold, cool to room temperature, then refrigerate for at least 2 hours until fully set.