Preheat oven to 350. Butter a 10-inch springform pan, lining bottom with wax paper.
Stir butter and chocolate in a heavy sauce pan over low heat until melted. Or use a double boiler.
Mix sugar and cocoa in a separate bowl.
Add eggs to sugar mixture and whisk until blended.
Whisk the melted chocolate into sugar egg mixture
Pour into the prepared pan
Bake until a toothpick comes out clean - at least 45 minutes
Cool cake on a rack completely. Run a knife around the perimeter to loosen the sides, then release the pan.
Make day ahead and store in the refrigerator.
Top with powedered sugar and raspberries