Prepare and bake one batch of cream cheese pastry tart shells.
Lemon Tart Filling
In a medium bowl beat the butter and sugar with an electric mixer for about two minutes, just like you do to make cookies.
Slowly add the eggs then beat for one more minute.
Stir in the lemon juice. The mixture will look curdled, but it will smooth out as it cooks.
Place the mixture in a medium sauce pan and cook over low heat until it's smooth. Increase the heat to medium and cook, continuously stirring, until the mixture thickens. The mixture should stick to the spoon slightly.
If there are any lumps, strain through a sieve.
Let the mixture cool in the pot for 15-20 minutes
Fill the cool tart shells 3/4 full with your lemon filling
Place the tarts in the fridge and the lemon filling will thicken more as it cools
Notes
These are best if kept in the fridge in a lidded container until ready to serve. For any left over filling, it is delicious on toast or ice cream!