PREHEAT oven to 350° F. Place 12 2 1/2-inch foil bake cups on baking sheet with sides. Place 1 piece of cookie dough in each cup.
BAKE for 12 to 14 minutes or until just baked and light golden brown. Remove cups to wire rack to cool completely.
PLACE 1 1/2 cups morsels and milk in large, microwave-safe bowl. Microwave on HIGH (100%) power for 1 minute; STIR. Morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until melted. Cool to room temperature, about 20 minutes.
RESERVE 1/2 cup whipped topping; refrigerate. Combine remaining whipped topping and vanilla extract in medium bowl. Gently fold half of the whipped topping mixture into chocolate mixture. Add remaining whipped topping mixture; mix lightly. Spoon over cookie bases in muffin cups. Refrigerate for 1 hour.
FOR GARNISH AND TO SERVE:
LINE baking sheet with wax paper.
PLACE remaining morsels in heavy-duty plastic bag. Microwave on HIGH (100%) power for 30 seconds; knead. Microwave at additional 10- to 15-second intervals, kneading until smooth. Cut tiny corner from bag. Drizzle 12 squiggly designs about 2- to 3-inches square onto prepared baking sheet. Refrigerate until chocolate is firm, 5 to 10 minutes.
TOP each mousse cup with a small dollop of reserved whipped topping. With tip of knife, gently remove drizzles from wax paper and insert, standing up into dollops. Serve immediately.