Zest the lemons to obtain about 1 tablespoon of zest.
Juice the lemons to get 1 cup of fresh lemon juice.
In a heatproof bowl, whisk together the eggs and sugar until combined.
Add the lemon juice and zest to the egg mixture and stir to combine.
Place the bowl over a pot of simmering water and stir continuously until thickened.
Add the cubed butter and stir until melted and incorporated.
Remove from heat and strain the curd through a fine sieve.
Transfer the lemon curd to clean jars and let it cool to room temperature.
Refrigerate for at least an hour before serving.