Add 2 inches of water to the bottom pot of a double boiler over high heat.

Once the water starts to boil, reduce to low heat.

Add egg yolks, sugar, lemon zest, lemon juice, and salt to the top pot of the double boiler.

Whisk constantly while cooking for about 10 minutes or until the mixture becomes thick.

Remove the double boiler from heat. Add cubed butter into the pot and whisk until the butter has melted.

Pour the cud into a bowl and place a piece of plastic wrap on top, making sure that it touches the top of the curd. Let it cool at room temperature and then remove the plastic wrap.

Serve and enjoy! (You can store it in an air-tight container in the fridge for 7-10 days)