Melt ½ of unsalted butter over medium heat and slowly mix it with crumbled biscuits in a food processor until you get a consistency that is not too solid nor soft. You should be able to mold the mixture and pick it up with a spoon without problems.
Add the biscuit-butter mixture to the bottom of your jars to form the bottom layer. (The layers height can be your personal preference.)
Mix heavy cream, cream cheese, lemon, orange and lime juice in a food processor or a blender (or any type of mixer). Add in lemon zest from 1 lemon. Add a pinch of salt.
Fill the jars with the cream cheese mixture until near the top. Make sure to leave space for the final layer of lemon jelly!
Separate egg yolks from the egg whites. Over medium heat mix the egg yolks with lemon juice until the mixture starts to thicken enough to coat the spoon. Optional: Prepare the gelatine according to the instructions on the package and mix it with the egg-lemon mixture.
Add the lemon mixture to the jars as the final layer and leave in the fridge for a few hours until it cools or the gelatine thickens.
Optional: Add whipped cream on top of the cheesecake jars and decorate to your liking.
Notes
You can keep this dessert in the fridge for 3 days.