PREHEAT oven to 350°F. Beat cream cheese and 1/2 cup softened butter in large bowl with electric mixer on medium speed until well blended. Add flour; mix well. Shape dough into ball, adding additional flour if dough is sticky. Divide into 48 balls. Place 1 ball in each of 48 lightly greased miniature muffin pan cups; press dough firmly onto bottom and 3/4 up side of each cup to form shell. Cover and refrigerate shells while preparing filling.

BEAT egg, sugar, 1 Tbsp. melted butter and the vanilla in medium bowl with wire whisk until well blended. Chop 4 of the chocolate squares; sprinkle evenly into shells. Top each with 1 tsp. of the pecans; cover evenly with the egg mixture.

BAKE 25 to 30 minutes or until lightly browned. Cool in pan on wire racks 30 minutes; remove tarts from pans. Melt remaining 2 chocolate squares as directed on package; drizzle over tarts. Let stand until chocolate is set. Store in tightly covered container in refrigerator.