Preheat the oven to 350 degrees.
Line the inside bottom of a 9″ Springform pan with a circle of parchment paper. Grease the sides of the pan. Set aside.
In a medium sauce pan, gently heat the cream over low heat. When the cream is fairly hot, melt the chocolate chips by adding them slowly to the pan as you whisk. Add the butter, in pieces. Whisk until the chocolate and butter are melted. Add the vanilla extract. As soon as the mixture is melted, smooth, and glossy, remove it from the heat.
Using a wire whisk attachment, beat the eggs, brown sugar and sea salt until the eggs are foamy and doubled in volume.
Slowly add the chocolate mixture to the eggs, and beat gently until combined. Pour the batter into the prepared cake pan. Bake in the center of a pre-heated oven for one hour, until the cake is set and cracked. It will appear a bit loose in the center, underneath. This is fine.
Place the cake pan on a wire rack to cool. When the cake is close to room temperature, lightly cover and chill the cake overnight. Before serving, gently loosen the cake from the sides of the pan using a thin flexible spatula. Release the Springform clasp and remove the ring. Place the cake on a cake plate. Dust with a sifting of powdered sugar.