preheat oven to 375. line the bottom of an 81/2" sprinform pan with parchment paper and spray with non-stick spray. heat chocolate and butter in a double boiler, stir until melted (or, heat in a microwavable bowl in microwave until melted).
put eggs and a pinch of salt in the bowl of an electric mixer, whip for 8 minutes until tripled in volume.
with a rubber spatula fold chocolate into egg mixture until well incorporated pour into springform pan, bake for 20 minutes.
center will be moist remove and let it cool 30 minutes before removing from pan and slicing.