In a small heavy saucepan over medium heat, whisk together the eggs, egg yolk, sugar, lime juice, and lime zest until evenly blended. Add the cubed butter and continue whisking constantly until the mixture thickens enough to coat the back of a spoon.

Transfer the lime filling to a bowl and let it cool slightly. Cover and refrigerate until thoroughly chilled.

In a separate bowl, beat the softened butter and cream cheese until smooth and creamy. Gradually mix in the flour until a soft dough forms. Cover and chill for 1 hour or until firm enough to handle.

Preheat the oven to 375°F. Roll the dough into 1-inch balls and press each into the bottom and up the sides of 24 ungreased miniature muffin cups. Prick the bottoms with a fork.

Bake for 15 minutes or until lightly golden. Let the shells cool in the pan for 5 minutes, then carefully remove to wire racks to cool completely.

Spoon the chilled lime curd into the cooled tart shells. Garnish with additional lime zest or grated white chocolate if desired. Store in the refrigerator.