Use this recipe when making our Lemon Poppy Seed Cake.
Whisk together lemon zest and juice, eggs, egg yolks, and sugar in a large, heavy saucepan. Cook, stirring constantly with a wooden spoon, over medium-low heat until mixture thickens, 12 to 15 minutes. Remove from heat, and stir in butter, 1 piece at a time, until melted. Transfer to a medium bowl. Cover with plastic wrap, pressing it directly on surface. Refrigerate until chilled, up to 1 day.