Citrus-Cinnamon Punch

• MAKE-AHEAD

ORANGE REDUCTION

1. 2 1/ 4 cups fresh orange juice
2. Strips of zest from 2 navel oranges
3. Three 3-inch-long cinnamon sticks, broken into pieces

PUNCH

1. 3 cups fresh orange juice
2. 2 cups fresh red grapefruit juice
3. 1 tablespoon grenadine syrup
4. 2 1/2 cups cold grapefruit soda (20 ounces)
5. Orange slices and ground cinnamon, for garnish

1. MAKE THE PUNCH In a saucepan, boil the orange juice, zest and cinnamon sticks over moderately high heat until reduced to 1 cup, 8 minutes. Strain and let cool.
2. In a large glass pitcher, combine the orange reduction with the orange and grapefruit juices and the grenadine. Stir well and refrigerate until chilled, about 1 hour. Just before serving, pour in the grapefruit soda. Dust the orange slices with cinnamon and serve in the punch.