Step 1

Add the sugar, egg, and lemon juice to a small sauce pot. Before placing the pot over the heat, whisk the ingredients together until smooth.

Step 2

Place the pot over medium heat and cook while whisking continuously. The mixture will become very frothy as you whisk. When the liquid becomes hot enough to cook the egg, the mixture will begin to thicken and no more liquid will separate from the foam. It will take about 5 minutes of whisking over medium heat for the mixture to thicken, but will vary depending on your cookware. The mixture should be thick enough to coat a spoon (see photos below).

Step 3

Remove the pot from the heat. Add one tablespoon of butter at a time, whisking until it has fully melted into the sauce before adding the next. As the butter is melted into the sauce, it will become less frothy and more silky in texture, and look more glossy rather than foamy.

Step 4

Once all of the butter has been whisked in, transfer the lemon curd to an air-tight container and refrigerate until completely cooled. The curd will thicken further upon cooling.