For the Tassie Cups: Place all of the ingredients in a food processor and pulse until the mixture forms a ball. Wrap in plastic wrap and chill until firm, about 1 hour.
Preheat the oven to 350 degrees F.
Form the pastry into 24 small balls; press with fingers into the bottom and up the sides of an ungreased mini muffin tin.
Bake for 15-20 minutes, until lightly browned.
For the Filling: In a stand mixer fitted with the paddle attachment, beat cream cheese, sugar, egg, lemon juice, and vanilla until completely smooth.
Carefully fill the cooled crusts using a spoon or cookie scoop.
Bake until filling is set and just beginning to color at the edges, 10 to 12 minutes.
Transfer muffin pan to a wire rack.. Let cool completely before serving.
The tassies may be stored in an airtight container, in the refrigerator for up to 5 days.