How to Make It
Prepare the Curd: Beat 2 cups granulated sugar and 1/2 cup butter with an electric mixer on medium speed until blended. Add eggs, 1 at a time, beating just until blended after each addition. Gradually add Key lime juice to butter mixture, beating at low speed just until blended after each addition. (Mixture may separate at this stage, but will emulsify as it is heated and whisked.)
Transfer mixture to a heavy 4-quart saucepan. Cook over medium-low, whisking constantly, until mixture thickens and just begins to bubble, 14 to 16 minutes. Remove saucepan from heat, and cool curd 30 minutes. Place heavy-duty plastic wrap directly on surface of warm curd (to prevent a film from forming), and chill until firm, about 4 hours. Refrigerate in an airtight container up to 2 weeks.
Prepare the Cream Cheese Pastry: Beat cream cheese, 1 cup butter, and 1/4 cup granulated sugar with a heavy-duty electric stand mixer on medium speed until creamy. Gradually add flour to butter mixture, beating at low speed just until blended after each addition. Shape dough into 60 (1-inch) balls, and place on a baking sheet; cover and chill 1 hour.
Preheat oven to 400°F. Place 1 chilled dough ball into each cup of lightly greased miniature muffin pans; press dough into bottoms and up sides of cups, forming shells.
Bake in preheated oven until lightly browned, 10 to 12 minutes. Remove shells from pans to wire racks, and cool completely, about 20 minutes.
Spoon about 1 1/2 teaspoons of the curd into each pastry shell. Cover filled shells, and chill until ready to serve. Just before serving, sprinkle filled shells evenly with powdered sugar and, if desired, garnish with lime zest.
You will have leftover curd. It is great spread on warm biscuits or scones, as a topping for pound cake, or as a dip for fresh fruit.