01 - Rinse cranberries and remove any stems or spoiled berries.
02 - Place cranberries, water, and lemon zest into a medium saucepan.
03 - Bring to a boil over medium-high heat, then reduce to a gentle simmer and cook for 10 minutes, stirring occasionally until cranberries burst and soften.
04 - Discard the lemon zest from the mixture.
05 - Press the mixture through a fine mesh sieve into a bowl, extracting all juice and pulp; discard solids.
06 - Return strained liquid to the saucepan. Add sugar and optional lemon juice, stirring to combine.
07 - Bring to a boil while stirring constantly, then reduce heat and simmer for 8 to 10 minutes until the liquid thickens to a jelly-like consistency.
08 - Remove from heat and let cool for 5 minutes.
09 - Pour into a serving dish or mold and cool to room temperature before refrigerating for at least 2 hours until fully set.