PREHEAT oven to 325° F. Paper-line 12 muffin cups.
COMBINE cookie crumbs and butter in small bowl. Press scant tablespoon onto bottom of each of prepared muffin cups. Bake for 5 minutes.
BEAT cream cheese, pumpkin, sugar, pumpkin pie spice and vanilla extract in small mixer bowl until blended. Add eggs; beat well. Pour into muffin cups, filling 3/4 full.
BAKE for 25 to 30 minutes. Cool in pan on wire rack. Remove tarts from pan; refrigerate. Garnish with sour cream. Place morsels in small, heavy-duty plastic bag. Microwave on HIGH (100%) power for 20 seconds; knead. Microwave at additional 10-second intervals, kneading until smooth. Cut tiny corner from bag; squeeze to drizzle over tarts.