In a heavy saucepan, combine the sugar and water. Bring to a boil over medium-high heat, stirring until the sugar dissolves. Reduce the heat to medium-low and simmer for 10 minutes. Add the zest, rosemary, and cloves. Simmer until the flavors are blended, about 5 minutes. Pour the syrup over the orange segments and toss. Refrigerate until well chilled, about 4 hours.
Sprinkle with orange liqueur. Place 1 slice of angel food cake in the bottom of 4 martini glasses. Top with 1 scoop frozen yogurt. Top with the oranges and garnish with a sprig of rosemary.
Yield: 4 servings