I love this stuff, but since I don't live in Chicago I don't know where to get it. So I decided to make it myself. It's very, very simple. Hope you enjoy!
1 cup sugar
2 cups water
1 cup lemon juice
1/4 lemon, deseeded and VERY thinly sliced (rind and all)
Bring to a boil the sugar and water. When it's boiling and almost thick, remove from heat, let cool 20 minutes then add the lemon juice and lemon slices. Cool overnight (on the counter or in the fridge; my fridge is overstuffed so I did it on the counter). Put in an ice cream maker and process for 20-30 minutes. Taste, a lot, then put the rest in a container and stick it in the freezer. Serves 1-4, depending on how greedy you are.