In a medium heatproof bowl, whisk together the sugar and eggs until well combined.

Add the fresh lemon juice and lemon zest to the bowl, stirring to incorporate.

Set the bowl over a pot of simmering water, creating a double boiler. Ensure the bottom of the bowl does not touch the water.

Cook the mixture, whisking constantly, until it thickens and coats the back of a spoon, about 10-15 minutes.

Remove the bowl from heat and stir in the butter pieces, one at a time, until fully melted and the curd is smooth.

Add a pinch of salt to enhance the flavor, mixing well.

Allow the lemon curd to cool to room temperature before transferring it to a clean jar or airtight container.

Refrigerate for at least 2 hours before using. The lemon curd will continue to thicken as it cools.