Break chocolate into pieces. Melt pieces in heavy saucepan with butter, until smooth (or microwave on medium for 2 1/2-3 minutes; stir til smooth). Beat egg yolks a few minutes with 2 tbsp. of sugar and vanilla. REmove melted chocolate from heat; using wire whisk, quickly stir in beaten yolks. Beat egg whites with salt, greadually adding remaining sugar, beating until soft peaks form. Place chocolate mixture in a large bowl with beaten egg white on top. Using wire whisk, carefully combine the two mixtures; do not overmix.
Cut parchment paper to fit bottom of a 9-inch springform pan. Butter bottom of pan and top of paper. Spread batter into prepared pan. Bake on lower shelf of 350 degree oven for 30-35 minutes, until cracked on top and a toothpick comes out clean from center. Cool on wire rack. Cake will shrink as it cools. Remove pan and loosen cake from paper. Garnish with whipped cream and fresh raspberries. 12-16 servings.