How to Make It
In a small bowl, sprinkle the gelatin over the lemon juice and let stand until softened, about 5 minutes.
In a medium saucepan, combine the sugar with 1 1/2 cups of water and bring to a boil. Simmer over moderate heat until the sugar is dissolved, 2 to 3 minutes. Remove from the heat and whisk in the lemon juice mixture. Let cool completely, then refrigerate until well chilled, about 2 hours.
In a blender, combine the lemon mixture with the milk and sorrel and puree until almost smooth, about 30 seconds. Strain the mixture through a fine sieve into a bowl and stir in the lemon zest.
Pour the sherbet mixture into an ice cream maker and freeze according to the manufacturer’s instructions. Transfer to an airtight container, cover and freeze the sherbet until it is firm, at least 2 hours, before serving.
Variation: For Lemon & Fresh Mint Sherbet, replace the sorrel leaves with 1/2 cup of lightly packed mint leaves.