Make the Crust
Mix crushed biscuits (digestive biscuits or graham crackers work great) with melted butter until well combined. Press the mixture firmly into the bottom of a 24cm (9-inch) pie pan. Use the back of a spoon to pack it down evenly. Set aside.
Dissolve the Jelly
In a small bowl, dissolve the lemon jelly packet in 1/2 cup boiling water, stirring until completely dissolved. Add the lemon juice and grated lemon rind. Set aside to cool slightly.
Make the Filling
In a separate bowl, mix the cream cheese and sweetened condensed milk together until smooth and well combined. You can use a hand mixer or whisk vigorously.
Combine Everything
Add the jelly mixture and vanilla extract to the cream cheese mixture. Mix well until everything is fully combined and smooth with no lumps.
Chill and Set
Pour the filling into the prepared crust. Place in the refrigerator to set for 4-6 hours, or preferably overnight. The cheesecake should be firm before slicing.