1/2 tsp unflavored gelatin
1/2 cup fresh lime juice [I used key limes]
7 tbsp sugar
1 large egg
1 egg white
2 tsp rum [I used mango-flavored rum]
One 3-by-1-inch strip lime zest
In a small bowl, sprinkle the gelatin over 2 tbsp of the lime juice. Set aside to soften.
In a medium stainless steel bowl, or the top of a double boiler, combine the remaining lime juice and the sugar, egg, egg white, and zest. Set the bowl over, but not in, simmering water. (Although the curd could be cooked directly over low heat in a heavy saucepan, using a water bath ensures that it doesn't overcook.) Whisk constantly until the curd is thick and coats the back of a spoon, about 5 minutes. Stir in the gelatin mixture and cook for 1 minute longer. Strain into a medium bowl and allow to cool to room temperature, whisking occasionally. Transfer the curd to a jar, cover, and refrigerate until ready to use. The curd will keep for about 1 week.
To translate this recipe back to the traditional lemon curd just replace the lime juice and zest with lemon and omit the rum.
To fill the lemon cake, split the cooled cake layer horizontally in half with a bread knife. (I got scared at this point because the cake is so thin, I thought I'd end up with nothing but crumbs, but Jim took over and it sliced really easily.) Spread the bottom layer with Lime Curd. Replace the top layer and sift the confectioner's sugar over the top. When serving, pour some of the lemon syrup around each slice.
-A New Way to Cook, Sally Schneider