Lemon Curd Cupcake Filling

Combine sugar, cornstarch and water in saucepan over medium heat. Stir constantly until mixture thickens and comes to a boil, 3–4 minutes.

Boil, stirring, for 1 minute more.

Remove from heat. Spoon about 1/2 cup of the hot mixture into a small bowl with egg yolks and stir quickly until combined.

While stirring, pour the egg mixture back into the saucepan. Return to medium heat and cook, stirring, until thickened and lemon colored, 1–2 minutes.

Remove from heat and stir in butter, lemon juice, and lemon zest.

Let cool, then press plastic wrap onto surface to prevent skin from forming. Refrigerate.