Preheat oven to 300F. Prepare a 9-inch cake round with pan spray and dust with cocoa.
Place chocolate and butter in a stainless steel bowl. Place bowl over a saucepan of simmering water (do not allow bottom of bowl to touch water). Stir chocolate frequently with a whisk until completely melted. Remove from heat. You can also melt chocolate in the microwave in a microwave-safe bowl at 10-second intervals, stirring occasionally, until chocolate is melted. Set aside to cool slightly. Reserve.
Using an electric mixer, whip egg yolks, 6 tablespoons of sugar, rum or espresso, vanilla extract, and salt on medium-high speed until pale and very thick – approximately 3-5 minutes. Gradually pour in the chocolate mixture and continue mixing until well blended.
In a clean dry bowl, using an electric mixer, whip the egg whites on medium-high speed until foamy – approximately 1 minute. Gradually add the remaining 3 tablespoons of sugar. Continue to beat until medium-firm peaks form – approximately 2 minutes. Fold half of the egg whites gently into the chocolate mixture. Fold in the remaining whites just until no streaks remain.
Pour the batter into the prepared pan and smooth the top. Bake until the torte puffs slightly and a toothpick inserted into the center comes out moist but not liquid – approximately 40 minutes. Do not overcook.
Transfer the pan to a rack and let cool for 30 minutes. Loosen cake from the pan and remove. Let the torte cool completely to room temperature, then cover and refrigerate, at least 4 hours or overnight.
Garnish the torte with raspberries, dust with powdered sugar, and serve.