MICROWAVE 1 cup chunks in medium, uncovered, microwave-safe bowl on HIGH (100%) power for 1 minute; STIR. Chunks may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring just until chunks are melted.
COMBINE flour, cinnamon, baking powder, salt and cayenne pepper in small bowl. Beat butter, granulated sugar and brown sugar in large mixer bowl until creamy. Add eggs and vanilla extract; beat well. Add melted chocolate; stir until blended. Gradually stir in flour mixture. Refrigerate for 2 hours.
PREHEAT oven to 350°F. Line baking sheets with foil.
SHAPE dough into 1 1/2-inch balls. Place 3 inches apart on baking sheets.
BAKE for 12 minutes or until cookies are puffed and centers are set but still soft. Immediately place remaining chunks, about 5 to 6 chunks per cookie, onto tops of cookies. Cool on baking sheets for 2 minutes; remove to wire racks. Allow chunks to soften and spread melted chocolate evenly over tops of cookies.
For a richer chocolate flavor, substitute three 4-ounce bars of NESTLE® TOLL HOUSE® CHOCOLATIER 53% Cacao Dark or 62% Cacao Bittersweet Baking Chocolate, broken into pieces, for the semi-sweet chocolate chunks.