In Italian supermarkets you can buy bottles of 95% proof alcohol, which the locals use to produce all sorts of infused liqueurs. Almost any kind of fruit is suitable (and even herbs such as basil), but limoncello, the liqueur made from lemons, is the most common.
Every family has its own recipe. This one was given to me by Michelina, a friend from Sorrento, and was devised by her grandmother.

Ingredients

8-10 lemons (ideally the Sorrentine variety form the spring harvest when they have the best perfume)
1 ltr 95% proof alcohol;
1 ltr water; 1 kg sugar.

Preparation

Peel the lemons and add the peel to a litre of alcohol. (The inside of the fruit can be used for other purposes). Leave for a week so that the flavours from the peel infuse into the liquid.
After a week boil the water and dissolve the sugar in it.
Allow this mixture to cool then add to the alcohol (now yellow and perfumed with lemon) having first removed the lemon peel.
Decant into bottles and serve chilled straight from the freezer.