How to Make It
In a bowl, rub the sugar with the lime zest using your hands.
In a nonreactive medium saucepan, whisk the lime juice with the eggs, egg yolk and lime sugar until well blended. Add the butter and whisk over moderate heat until small bubbles appear around the sides. Immediately remove from the heat and strain the lime cream through a fine sieve into a bowl.
Press a piece of plastic wrap directly on the surface of the lime cream and let cool completely, then refrigerate until chilled. The cream can be refrigerated for up to 2 weeks.