In a large bowl, beat cream cheese until it is light and fluffy.
Add in the powdered sugar, lemon juice, and salt and beat until everything is combined.
Gently fold in the whipped topping.
IF YOU ARE ADDING THE SHORTBREAD CRUST: Divide crushed shortbread cookies between 4 dessert cups. (This step is optional)
Equally divide lemon mousse into cups and refrigerate uncovered until thickened, (about 1 hour up 24 hours).
When ready to serve, top with remaining whipped topping and lemon wedges.