Preheat oven to 350 F. Line 2 (9 inch) pans with parchment, spray parchment with cooking spray.
Melt 6 oz chocolate as directed on package; cool.
Microwave 4 oz chocolate and butter in a large microwavable bowl on HIGH 1 – 1 ½ min or until butter is melted, stirring every 30 seconds. Stir until chocolate is completely melted, cool.