In 2-quart saucepan, mix 1 cup sugar and the cornstarch. Gradually stir in water, lemon zest and lemon juice until smooth. Cook and stir over medium-high heat. Heat to boiling; boil 1 minute, stirring constantly, until mixture is bubbly and thickened. Remove from heat.
In small bowl, beat egg yolks with whisk. Gradually beat about 1/2 cup hot mixture into egg yolks.
Gradually stir yolk mixture into hot mixture in saucepan. Cook over medium heat, stirring constantly, until mixture starts to gently boil. Cook 2 minutes longer, stirring constantly. Remove from heat transfer lemon curd in any glass bowl cover with clear wrap pressed onto the top of the curd to avoid a film developing, and refrigerate until cold.
Cover with lid and keep in refrigerator.
Use this lemon curd in lemon curd tart, lemon meringue pie, lemon mousse, lemon drizzle cake type recipe.
