In a heavy saucepan combine half-and-half, lemon zest and cinnamon stick over medium heat and bring to a simmer. Remove from heat and let steep for 10 minutes. Strain into a large bowl, discarding solids. Set aside and let cool.
Whisk egg yolks (or subsitute) and 1/2 cup sugar together in a large mixing bowl until thick and pale yellow.
Whisk in half-and-half.
Return mixture to saucepan and cook over medim low heat, stirring constantly with wooden spoon until thick (20-30 minutes). Remove from heat and strain into a large bowl and set aside. Cover and refrigerate until chilled (2-4 hours).
While custard is chilling, grease a cookie sheet with butter and set aside.
In a large saucepan, combine remaining sugar (1 cup) and 4 tablespoons water and bring to a simmer over medium low heat, swirling pot frequently until sugar carmalizes (20-30 minutes).
Immediately pour syrup onto prepared sheet, tilting pan to spread around so syrup is a thin layer. Set aside and let cool.
Crack carmamel into small pieces.
Stir into cooled custard.
Process in ice cream maker according to manufacturer's directions.