1. Line 10 muffin cups (2-1/2 inches in diameter) with paper bake cups. Reserve 1/2 cup chocolates. Place remaining 1-1/4 cups chocolates in small microwave-safe bowl; microwave at MEDIUM (50%) 1 minute or until melted when stirred. Mixture should be thick.
2. Coat inside pleated surfaces and bottoms of bake cups very thickly with melted chocolate, using a soft pastry brush. Refrigerate 10 minutes; recoat any thin spots with melted chocolate.* Refrigerate until firm, about 2 hours. Gently peel off paper; refrigerate until ready to fill.
3. Place marshmallows, milk, and pumpkin in medium microwave-safe bowl. Microwave at MEDIUM 1 minute; stir. Microwave an additional 30 seconds at a time, stirring after each heating, until mixture is melted and smooth. Stir in vanilla and pumpkin pie spice. Cool completely.
4. Beat powdered sugar and whipping cream until stiff; fold into pumpkin mixture. Fill cups with pumpkin mousse; garnish with reserved chocolates. Cover; refrigerate 2 hours or until firm. Cover; refrigerate leftovers. 10 servings.
* Note: If reheating is needed, microwave chocolate at MEDIUM 30 seconds; stir.