1 1/3 cups water
2/3 cup sugar
1 vanilla bean, split in half lengthwise
4 large navel oranges
2 large grapefruits
Combine the sugar, water and vanilla bean in a small saucepan. Place over medium heat and bring to a simmer. Stir frequently to dissolve the sugar completely. Remove from heat and let cool.
Section the oranges and grapefruit. Cut off each end of the fruit (blossom and stem ends). Next stand the fruit up on its cut end and slice down the contour removing the peel. Holding the fruit over a bowl cut along each segment letting them fall into the bowl.
Add the cooled syrup to the fruit and toss gently with a spoon. Cover and refrigerate until well cooled.
Serve in small bowls and garnish with mint sprigs.