- Heat oven to 350° F. Butter a 9-inch springform pan and dust with cocoa powder.
- In a medium saucepan, heat the butter with ¼ cup of the heavy cream over medium-low heat until the butter is melted. Add the chocolate and stir until melted and smooth; remove from heat.
- In a medium bowl, whisk together the eggs, granulated sugar, and cocoa powder. Whisk in the chocolate mixture.
- Transfer the batter to the prepared pan and bake until puffed and set, 35 to 40 minutes. Let cool in the pan for 1 hour. Run a knife around the edge of the cake before unmolding.
- Using an electric mixer, beat the remaining 1 cup of heavy cream with the crème fraîche and confectioners’ sugar until soft peaks form. Dust the cake with cocoa (or confectioners’ sugar) and serve with the whipped cream mixture.