Beat the cream cheese. In a medium bowl, beat the room-temperature cream cheese with the powdered sugar, vanilla, salt, and lemon juice until completely smooth, about 1 minute. Scrape down the sides of the bowl.
8 oz full-fat cream cheese, room temperature, 1/3 cup powdered sugar, sifted, 1 tsp vanilla extract, 1 tsp lemon juice, 1 pinch salt
Whip the cream. In a separate bowl, whip the cold heavy cream to medium peaks — when you lift the whisk, the peak should hold but gently flop over at the tip.
1/2 cup cold heavy cream
Lighten the base. Add about a third of the whipped cream to the cream cheese mixture and stir it in to loosen the base.
Fold in the rest. Add the remaining whipped cream and fold gently with a spatula until no white streaks remain. The mixture should be smooth and pipeable.
Taste and adjust. Taste the filling and fold in more powdered sugar or lemon juice if needed, using a spatula so you don't deflate it.
Fill the cups. Spoon or pipe the filling over the chilled crusts, dividing evenly between the 4 cups. Smooth the tops or leave them swirled.
Chill. Refrigerate for at least 2 hours so the filling firms up and the flavors come together. Overnight is even better.
Top and serve. Finish with fresh berries, fruit compote, lemon curd, crushed biscuit dust, or a drizzle of dark chocolate ganache.