Whisk the butter and sugar together until they combine.
Add the eggs to the butter and sugar mixture slowly and whisk until well blended.
Pour the lemon juice into the mixture. You can also add lemon zest to the mixture at this point, if you desire. Mix well.
Pour the mixture into a pot and place the pot on the stovetop. Turn the heat on the stove to medium or medium low.
Allow the mixture to come to a simmer. Continue to cook the mixture until the lemon curd reaches a temperature of 170 degrees F and coats a spoon. Be sure to stir the lemon curd during cooking to prevent burning or sticking.
Let the lemon curd cool completely.
Put the cooled lemon curd in a covered container and store in the refrigerator until ready to use.
Serve lemon curd on scones or toast, or use it in cookie, cake and tart recipes.
Don't allow the mixture to come to a boil or it can curdle.
Put lemon curd in an airtight container and this can be kept in the freezer for several months.