Pour 1 cup water into a small saucepan and add 1 cup of sugar. Over a low heat, stir mixture until sugar is dissolved. Then bring to a boil and boil for 1 minute. Remove syrup from heat and allow to cool.
Once sufficiently cooled add lemon zest and orange and lemon juice.
Beat egg whites and 1 teaspoon of sugar until foamy. Slowly add citrus syrup to egg whites. Whisk together until well combined.
Pour solution into an ice cream freezer and rotate freezer as you would if you were making homemade ice cream. Transfer the firm sorbet into a container and place in the freezer.
If you do not have an ice cream maker, pour the solution into a shallow dish and freeze until sorbet is frozen around the edges. Remove from freezer, mix until smooth and refreeze until almost solid. Repeat this process two more times.Just before you are ready to serve the sorbet, beat it briefly with a spoon to make it creamy.
Serve cold, garnished with slices of fresh orange.