Separate the yolks from the whites and place the yolks into a pot. Reserve the whites for another use.

Place the sugar into a bowl and zest the lemons into the bowl with the sugar. Mix the zest into the sugar with a rubber spatula to extract the oils and set aside for at least 15 minutes.

Juice the lemons, straining out the seeds.

Add the sugar into the pot with the yolks and whisk until pale and creamy. Add the lemon juice gradually while continuing to whisk.

Once the lemon juice is all mixed in, place the mixture over low heat and stir constantly with a whisk until the mixture thickens and then immediately remove from the heat.  

Strain the mixture through a fine sieve then add the cold, cubed butter and whisk until the butter is fully incorporated and the mixture is smooth.

Strain the mixture again through a fine sieve, to achieve a silky-smooth consistency.

For use as a pastry filling, pour into a bowl, cover the surface with plastic wrap to prevent a skin from forming and refrigerate for use within 2 days.  It makes a wonderful dessert filling for my sweet paste pastry shells.

To preserve the lemon curd in jars, sterilize jars and fill with the curd while it is warm.

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