Heat oven to 450°F. Unroll pie crusts on work surface. With rolling pin, roll each crust lightly into 12-inch round. With 3-inch round cutter, cut 24 rounds from crusts, rerolling scraps as necessary. Press 1 pie crust round in bottom and up side of each of 24 ungreased mini muffin cups, so edges of crusts extend slightly above sides of cups.
Bake 5 to 7 minutes or until very light golden brown; cool. Reduce oven temperature to 325°F.
Cut candy bars in half lengthwise; cut into 1/8-inch pieces; chop coarsely. Place candy bar pieces in bottoms of crust-lined cups, reserving some for garnish. In small bowl, beat cream cheese and sugar with electric mixer on medium speed until smooth. Beat in egg until well blended. Add sour cream and peanut butter, beating until mixture is smooth. Spoon 2 teaspoons cream cheese mixture over candy bar pieces in each tart.
Bake at 325°F 20 to 22 minutes or until center is set. Cool completely, about 30 minutes.
In 1-quart saucepan, heat whipping cream until very warm. Remove from heat; stir in chocolate chips until melted and smooth. Spread over top of each tart. Garnish with reserved candy bar pieces. Refrigerate 2 to 3 hours before serving. Cover and refrigerate any remaining tarts.