Preheat oven to 325ºF. Line a 6-inch springform pan** with parchment paper. Spray the parchment paper with nonstick spray. Wrap the bottom two inches of the pan tightly with aluminum foil. Set pan in a baking pan.

Combine chocolate and butter in a large stainless steel bowl set over a pot of barely simmering water. Stir until melted and smooth. Remove bowl from heat.

In a large bowl, beat eggs with an electric mixer until doubled in size, about 5 minutes. Beat in vanilla extract and salt.

With a large spatula, gently fold beaten eggs into chocolate mixture in three additions until no streaks of egg remain. Transfer batter to prepared pan. Smooth top of batter with a small offset spatula.

Pour 1 1/2 inches of boiling water into baking pan. Bake until top is set and internal temperature*** reaches 140ºF, about 28-37 minutes.

Remove cake pan from water bath. Cool to room temperature then cover and refrigerate for at least 4 hours (or up to overnight, but cake is best served the day it's made).

Remove cake from pan when chilled and set. Top with powdered sugar and fresh raspberries.

To serve, remove cake from refrigerator at least 30 minutes before serving and serve at room temperature for best texture. Serve with raspberry sauce.

Purée raspberries in blender or food processor. Pass purée through a fine mesh sieve**** to remove seeds.

In a small bowl, whisk together water and cornstarch.*****

In a small saucepan, heat raspberry purée with sugar and cornstarch slurry to a boil over medium heat. Turn heat down to low and simmer until slightly thickened, about 2-3 minutes.