Gather all ingredients and zest the lemons before juicing them.
In a medium saucepan, whisk together the sugar and eggs until smooth.
Stir in the lemon juice and lemon zest until well combined.
Place the saucepan over medium heat. Stir constantly with a wooden spoon or a spatula, making sure to scrape the sides and bottom of the pan, to prevent the mixture from curdling.
As the mixture heats up, add the melted butter. Continue to stir and cook until the mixture thickens and can coat the back of the spoon. This should take about 7-10 minutes.
Once thickened, remove the saucepan from heat and strain the lemon curd through a fine mesh sieve into a bowl to remove any bits of cooked egg and zest.
Allow the lemon curd to cool. Once cooled, transfer it to a jar or an airtight container. Refrigerate until ready to use. It will keep in the refrigerator for up to two weeks.
