Preheat oven to 375 degrees F. and line an 8 inch springform or tart pan with parchment paper and spray with non stick cooking spray.
Cut up chocolate into small pieces and place over a double boiler with butter. Stir until melted. Transfer to a medium mixing bowl and let cool for 5 minutes.
Whisk in sugar, eggs and cocoa powder. Pour into prepared springform pan and bake for 30-35 minutes or until baked through. Let cool for 10 minutes then release springform pan. Let cool completely before cutting into wedges.
Dust with powdered sugar and top with raspberries. Serve room temperature.