In a medium saucepan, add the eggs, sugar, lemon juice, and salt.
Whisk everything together until smooth.
Put the saucepan on the stove over medium low heat.
Keep whisking all the time so it does not stick or burn. Make sure to stir the sides and corners of the pan too.
After about 10 minutes, the mixture will become thick. It should coat the back of a spoon.
Do not let it boil. If it starts bubbling too much, lower the heat.
Remove the pan from the heat.
Add the diced butter and stir until it melts completely and becomes smooth.
Pour the lemon curd into a bowl or jar.
Place plastic wrap directly on top of the curd so it does not form a skin.
Let it cool completely for about 2 hours.
While it cools, make the syrup.