Preheat oven to 350 degrees F (175 degrees C). Line the bottom of a 9 inch round cake pan with parchment paper.
Bring butter, espresso, and sugar to a boil in a medium saucepan, stirring to dissolve sugar.
Place chocolate in a large bowl, and add boiling hot espresso mixture. Whisk until smooth. Cool slightly. Whisk in eggs. Pour batter into prepared pan.
Place cake pan in a roasting pan. Pour enough hot water into the roasting to come half way up the sides of the cake pan. Bake until center of cake is set, and a tester inserted comes out clean with a few moist crumbs attached, about 1 hour. Remove from water. Chill overnight.
Puree raspberries in processor. Chill. Serve with chilled cake.