In a microwave, melt chocolate chips and butter; whisk until smooth. Cool slightly. , In a large bowl, beat sugar and eggs. Stir in vanilla and chocolate mixture. Gradually add flour; stir in walnuts. Fill paper-lined miniature muffin cups almost full. , Bake at 350° for 20-23 minutes or until a toothpick inserted in the center comes out clean. Cool for 5 minutes before removing from pans to wire racks to cool completely., For ganache, place chocolate chips in a small bowl. In a small saucepan, bring cream just to a boil. Pour over chocolate; whisk until smooth. Cool for 30 minutes or until ganache reaches a spreading consistency, stirring occasionally. Spread over brownie cups.