Place 2 eggs yolks, two eggs and sugar in a medium saucepan and whisk until smooth. This step is important to avoid any lumps or pieces of egg white in your lemon curd.
Place the saucepan over low heat. Add the butter, lemon juice and lemon zest and whisk until well combined. Continue to whisk the mixture over low heat until the lemon curd thickens. This will take about 7 to 10 minutes.
Strain the zest into sterilised jars using a fine mesh strainer. (If you don't mind some texture from the lemon zest, you can skip the strainer and pour lemon curd directly into the jars).
Place lids on jars and allow to cool slightly on bench before refrigerating.