An all-citrus terrine is a refreshing dessert.
Combine the sugar, star anise, cinnamon sticks, and 1 1/4 cups water in a small saucepan. Bring to a boil over medium-high heat. Reduce to a simmer, and cook 5 minutes. Remove from heat; allow syrup to cool.
Using a paring knife, carefully remove peel, pith, and outer membranes from all citrus. Carefully slice each segment of pulp from the membranes into a sieve set over a large bowl. Transfer segments to another bowl, removing any seeds and being careful not to break segments. Set the citrus segments aside; reserve juice for another use.
Strain cooled syrup into a medium bowl. Sprinkle gelatin over syrup; allow to dissolve, 2 minutes. Return to saucepan; place over low heat, stirring, until gelatin has fully dissolved. Remove from heat; set aside to cool.
Coat a 4 1/2-by-9-inch loaf pan or 5-cup mold with cooking spray; line with plastic, allowing 6 inches to overhang on all sides. Fill pan with reserved citrus segments. Pressing firmly on fruit, tilt the pan, draining excess juice. Pour gelatin mixture over fruit, poking with a skewer so mixture runs into the corners. Carefully fold excess plastic over top, and chill until set, 6 hours or overnight.
To serve, unfold plastic; place a platter on top. Carefully invert both; remove pan, holding plastic in place on platter. Remove the plastic. Slice; serve with lemon sorbet.