The foam comes from an egg white.  If you are little worried pick up some pasteurized eggs.

Lime Pie – The Cocktail (from February 2010 issue of Food and Wine)

• 2 ounces light rum
• 3/4 ounce simple syrup
• 1 ounce lime juice
• 1 egg white
• Shaker filled with ice

Simple Syrup

If you need to make simple syrup.  Simmer 1 cup of water with 1 cup of sugar until the sugar is fully dissolved.  Let cool and use.  Refrigerate any leftovers.

The Drink

Fill a cocktail shaker with ice.

Add the rum, simple syrup, lime juice and egg white.  Shake until the the drink is chilled and frothy.

Strain into a coup or wide mouthed glass.  Garnish with a lime wedge.

Remember that if you are a little uneasy using raw egg whites, you can purchase pasteurized eggs at most supermarkets.

This drink was awesome.  If it were not for the fact that I only had two limes in the house, Dana and I would have pounded down a dozen of these.  They were so tasty.  I am going to have to purchase a case of limes.  Love this drink.

Variation

A little different play would be to make a Key Lime Cocktail.  To do this keep all of the ingredients the same except use 1 oz of simple syrup instead of 3/4oz.  Also only use  3/4 oz of key lime juice instead of 1 oz.  Key limes are more acidic and tart.  Less juice and more simple syrup will offset the flavor difference.