Preheat the oven to 325°F with a rack set in the center.

Spray a 9-inch springform pan with nonstick cooking spray. Set aside.

Place the chopped chocolate and butter in a large microwave-safe mixing bowl. Microwave on high in 30-second increments, stirring between each, until the chocolate is fully melted and smooth, about 2 1/2 minutes total. Allow the mixture to cool at room temperature for 5 minutes.

Meanwhile, place the eggs, granulated sugar, vanilla extract, and salt in a large mixing bowl. Beat with a mixer on high speed until the mixture is pale, foamy, and nearly doubled in volume, 3-4 minutes.

Pour the egg mixture into the melted chocolate. Fold gently with a rubber spatula until the batter is just smooth and no yellow streaks of egg remain.

Pour the batter into the prepared springform pan.

Bake the cake until it is set (no jiggling when it's gently shaken) and a toothpick inserted in the center comes out slightly moist but with no crumbs, about 50 minutes. An instant-read thermometer inserted into the middle of the cake (not touching the pan) should reach 200°F.

Check to see that cake is done. Remove from oven or add time as needed.

Allow to cool on a wire rack at room temperature for 10 minutes, then transfer to the refrigerator. Chill for at least 4 hours before serving.

Run a knife around the edge of the cake. Release the sides of the springform pan. Use a fine-mesh sieve to dust the top of the cake with a generous coating of powdered sugar. Top with raspberries if you like. Chill any leftovers airtight up to 3 days.