Add the butter to a saucepan on very low, then whisk in the swerve. Whisk in the eggs, then the salt, lemon juice and lemon zest. Turn the heat up to medium-low and cook for about 6-8 minutes or until it thickens enough to coat the back of a spoon.
The key to this curd coming out smooth and creamy, is to whisk the entire time!
Remove from the heat and cover with plastic wrap, making sure it's actually touching the curd (to prevent a skin from forming). Chill in the fridge and enjoy!
If you don't like your lemon curd too tart, you can use a little less lemon juice and zest.