In a medium saucepan, over medium-high heat, combine butter, sugar, lemon juice and lemon zest. Cook, stirring constantly, until all butter is melted and sugar is dissolved about 4 minutes.
In a heatproof bowl, whisk eggs. Continue whisking while pouring in about 1 cup of hot lemon liquid. Once combined transfer egg mixture back to saucepan, and continue to cook, over medium-low heat, stirring constantly until mixture thickens and coats the back of a spoon, about 5 minutes.
Cover surface directly with plastic wrap. Cool in fridge until ready to serve with Strawberry and Lemon Shortcake.