Gelato al limone (Lemon gelato)

What could be more refreshing after a rich meal than a lemon gelato?
This recipe appears in the current issue of Taste Italia (June 2011).
serves 6
prep 15 mins, plus freezing
cooking 15 mins
If your lemons are very sour, you may wish to reduce the lemon juice by a quarter or half.
350 ml milk
180g sugar
150 ml heavy cream
juice of 5 lemons
mint sprigs, to garnish
In a saucepan, heat the milk over a medium heat to just under a boil. Add sugar and immediately remove from the heat. Stir until the sugar dissolves. Slowly stir in the cream, then the lemon juice.
Plunge the pan into a bowl of ice cubes and stir until the mixture is cold. Transfer to an ice cream maker and churn according to instructions.
Alternatively place in the freezer, stirring every so often with a fork to break up the ice crystals. Serve with mint sprigs.
Recipe created by Aurora Baccheschi Berti.

My take on the recipe: first of all I would like to know what milk is better for the recipe. Does it have to be full fat milk, will it then take less time to set? I used semi skimmed milk, and it took a long time for the gelato to set. Again, would have been helpful if the time of the freezer setting version was printed in the magazine.
I used 4 lemons for my gelato. I was worried that the gelato will be too sour, but it turned out to have a very delicate lemon flavour. It is a brilliant gelato, and I will definitely make it again.