- 1 pound Seville oranges or tangelos, scrubbed
- 3 small or 2 large lemons, scrubbed
Combine whole oranges and lemons with 6 cups water in a large saucepan; bring to a boil. Reduce heat to medium, cover with lid slightly ajar, and simmer until fruit is very tender, about 2 hours. Using a slotted spoon, transfer fruit to a medium bowl; let cool. Reserve cooking liquid in pan.
Place 4 layers of cheesecloth cut into 18x18" squares inside a large bowl. Cut each fruit in half. Spoon flesh and as much white pith as possible out of peel and into cheesecloth in bowl; add any accumulated juices from bowl with fruit. Gather up edges of cheesecloth and squeeze juice from fruit into large bowl; discard cheesecloth and pulp. Slice orange peel into thin strips (discard lemon peel).
Simmer reserved fruit cooking liquid in saucepan until reduced to 3/4 cup, 15-20 minutes; strain and return to pan. Attach a candy thermometer to side of pan. Add sugar and reserved juice in bowl. Bring to a boil, stirring until sugar dissolves. Boil until thermometer reaches 215°, about 10 minutes. Let cool for 15 minutes; stir in peel. Transfer to 2 clean pint jars. Let cool. Cover and chill. DO AHEAD Can be made 2 weeks ahead. Keep chilled.