How to Make It
Stir together first 4 ingredients in a small, heavy saucepan; add egg, stirring until blended.
Cook mixture, stirring constantly, over low heat, 10 to 12 minutes or until mixture thickens slightly (cooked mixture will have a thickness similar to unwhipped whipping cream) and begins to bubble around the edges. Remove from heat. (The curd should be brushed immediately over cake, as mixture will continue to thicken as it cools.)